Synthesis of single crystalline spinel LiMn2O4 nanowires for a lithium ion battery with high power density

Oxides Induced Preferential Growth of {110} Planes for Superior Performance Single-Crystal LiMn2O4 through Solid-State Process

Polycrystalline lithium manganese oxide (LMO) is known to suffer from severe surface structure degradation and electrochemical polarization due to its mixed crystal plane orientations. A hexagonal prism single-crystal LMO (LMOS-HP), engineered through the SrO-induced preferential growth effect, features the most stable {111} top surfaces and the fastest Li+ diffusion {110} side surfaces, effectively addressing these challenges. Consequently, LMOS-HP exhibits superior electrochemical capability, with only 0.021% capacity fading per cycle after 500 cycles and achieves a discharge capacity of 81.9 mAh g-1 at 20C. This innovative design offers a promising approach for tuning surface crystal orientation to improve performance.

Theoretical study on the effect of torsional deformation on WTe2 as a cathode material for calcium ion batteries

CONTEXT

In this study, the electronic structure and diffusion barrier of the Ca-adsorbed WTe2 system under different torsion angles were calculated based on the first-principles method. The results show that the structure and properties of the pure WTe2 system and Ca-adsorbed WTe2 system are affected by torsional deformation. When the torsion angle is 6°, the intrinsic WTe2 changes from a direct band gap to an indirect band gap. The torsional deformation does not change the metallicity of the Ca-adsorbed WTe2 system. The Ca-d state electrons contribute to the electron density of WTe2. The calculation of the diffusion barrier shows that the torsion deformation promotes the diffusion of calcium on the surface of WTe2. This study provides a theoretical basis for the regulation of electrode materials.

METHODS

In this study, Materials Studio 8.0 software was used to construct the WTe2 model and Ca-adsorbed WTe2 model, and CASTEP module was used for first-principles calculation.

Flexible Ti3C2Tx/Nanocellulose Hybrid Film as a Stable Zn-free Anode for Aqueous Hybrid Zn-Li Batteries

Aqueous zinc-based batteries are a very promising technology in the post-lithium era. However, excess zinc metals are often used, which results in not only making a waste but also lowering the actual energy density. Herein, a Ti₃C₂T_x/nanocellulose (derived from soybean stalks) hybrid film is prepared by a facile solution casting method and employed as the zinc-free anode for aqueous hybrid Zn-Li batteries. Benefiting from the ultra-low diameter and rich hydroxyl groups of nanocellulose, the hybrid film exhibits better mechanical properties, superior electrolyte wettability, and more importantly, significantly improved zinc plating/stripping reversibility compared to the pure Ti₃C₂T_x film. The hybrid film also dramatically overwhelms the stainless steel as the electrode for reversible zinc deposition. Further analysis shows that the hybrid film can lower the zinc deposition overpotential and promote the desolvation process of hydrated Zn²⁺ ions. In addition, it is found that hexagonal Zn thin flakes are horizontally deposited onto the hybrid film owing to the low lattice mismatch between the Ti₃C₂T_x surface and the (002) facet of Zn. Consequently, zinc dendritic growth and accompanied harmful side reactions can be considerably inhibited by the hybrid film, and the assembled Zn-Li hybrid batteries exhibit excellent electrochemical performances. This work might inspire future work on zinc-based batteries.

Synthesis and Surface Coating of LiMn₂O₄ Nanorods for the Cathode of the Lithium-Ion Battery

MnO₂ nanorods are prepared using a hydrothermal method, and used as precursors for the synthesis of LiMn₂O₄ nanorod-based active material for the cathode of lithium-ion batteries. The effects of additives, pressure, reactant concentration in the solution, and reaction time during the hydrothermal synthesis on the morphology of MnO₂ are examined. For the synthesis of the LiMn₂O₄ nanorods, two synthetic methods, hydrothermal processing of the MnO₂ precursor in a Li-containing solution, and the solid-state reaction of the precursor with LiOH·H₂O powder are tested. The morphological and electrochemical properties of the resulting materials are then analyzed. The rate and cycle performances of the LiMn₂O₄ nanorods are considerably improved by a composite coating of Li-ion-conductive Li₂O-2B₂O₃ and electrically conductive carbon. Because the conductive properties of these coating materials can be obtained with low crystallinity of them, superior coating performance is attainable with relatively low-temperature of after heating, which is advantageous in preserving the morphology of LiMn₂O₄ nanorods.

Understanding and Calibration of Charge Storage Mechanism in Cyclic Voltammetry Curves

Noticeable pseudo-capacitance behavior out of charge storage mechanism (CSM) has attracted intensive studies because it can provide both high energy density and large output power. Although cyclic voltammetry is recognized as the feasible electrochemical technique to determine it quantitatively in the previous works, the results are inferior due to uncertainty in the definitions and application conditions. Herein, three successive treatments, including de-polarization, de-residual and de-background, as well as a non-linear fitting algorithm are employed for the first time to calibrate the different CSM contribution of three typical cathode materials, LiFePO₄ , LiMn₂ O₄ and Na₄ Fe₃ (PO₄ )₂ P₂ O₇ , and achieve well-separated physical capacitance, pseudo-capacitance and diffusive contributions to the total capacity. This work can eliminate misunderstanding concepts and correct ambiguous results of the pseudo-capacitance contribution and recognize the essence of CSM in electrode materials.

Supercapattery electrode materials by Design: Plasma-induced defect engineering of bimetallic oxyphosphides for energy storage

Although transition metal hydroxides are promising candidates as advanced supercapattery materials, they suffer from poor electrical conductivity. In this regard, previous studies have typically analyzed separately the impacts of defect engineering at the atomic level and the conversion of hydroxides to phosphides on conductivity and the overall electrochemical performance. Meanwhile, this paper uniquely studies the aforementioned methodologies simultaneously inside an all-in-one simple plasma treatment for nickel cobalt carbonate hydroxide, examines the effect of altering the nickel-to-cobalt ratio in the binder-free defect-engineered bimetallic Ni-Co system, and estimates the respective quantum capacitance. Results show that the concurrent defect-engineering and phosphidation of nickel cobalt carbonate hydroxide boost the amount of effective redox and adsorption sites and increase the conductivity and the operating potential window. The electrodes exhibit ultra-high-capacity of 1462 C g^-1, which is among the highest reported for a nickel-cobalt phosphide/phosphate system. Besides, a hybrid supercapacitor device was fabricated that can deliver an energy density of 48 Wh kg^-1 at a power density of 800 W kg^-1, along with an outstanding cycling performance, using the best performing electrode as the positive electrode and graphene hydrogel as the negative electrode. These results outperform most Ni-Co-based materials, demonstrating that plasma-assisted defect-engineered Ni-Co-P/PO_x is a promising material for use to assemble efficient energy storage devices.

Understanding Degradation at the Lithium-Ion Battery Cathode/Electrolyte Interface: Connecting Transition-Metal Dissolution Mechanisms to Electrolyte Composition

Lithium transition-metal oxides (LiMn₂O₄ and LiMO₂ where M = Ni, Mn, Co, etc.) are widely applied as cathode materials in lithium-ion batteries due to their considerable capacity and energy density. However, multiple processes occurring at the cathode/electrolyte interface lead to overall performance degradation. One key failure mechanism is the dissolution of transition metals from the cathode. This work presents results combining scanning electrochemical microscopy with inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to examine cathode degradation products. Our effort employs a LiMn₂O₄ (LMO) thin film as a model cathode to monitor the Mn dissolution process without the potential complications of conductive additive and polymer binders. We characterize the electrochemical behavior of LMO degradation products in various electrolytes, paired with ICP and EPR, to better understand the properties of Mn complexes formed following metal dissolution. We find that the identity of the lithium salt anions in our electrolyte systems [ClO₄^-, PF₆^-, and (CF₃SO₂)₂N^-] appears to affect the Mn dissolution process significantly as well as the electrochemical behavior of the generated Mn complexes. This implies that the mechanism for Mn dissolution is at least partially dependent on the lithium salt anion.

Atomic Insights into Ti Doping on the Stability Enhancement of Truncated Octahedron LiMn2O4 Nanoparticles

Ti-doped truncated octahedron LiTi_xMn_2-xO₄ nanocomposites were synthesized through a facile hydrothermal treatment and calcination process. By using spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM), the effects of Ti-doping on the structure evolution and stability enhancement of LiMn₂O₄ are revealed. It is found that truncated octahedrons are easily formed in Ti doping LiMn₂O₄ material. Structural characterizations reveal that most of the Ti⁴⁺ ions are composed into the spinel to form a more stable spinel LiTi_xMn_2−xO₄ phase framework in bulk. However, a portion of Ti⁴⁺ ions occupy 8a sites around the {001} plane surface to form a new TiMn₂O₄-like structure. The combination of LiTi_xMn_2−xO₄ frameworks in bulk and the TiMn₂O₄-like structure at the surface may enhance the stability of the spinel LiMn₂O₄. Our findings demonstrate the critical role of Ti doping in the surface chemical and structural evolution of LiMn₂O₄ and may guide the design principle for viable electrode materials.

Efficient Direct Recycling of Degraded LiMn2O4 Cathodes by One-Step Hydrothermal Relithiation

Due to the large demand of lithium-ion batteries (LIBs) for energy storage in daily life and the limited lifetime of commercial LIB cells, exploring green and sustainable recycling methods becomes an urgent need to mitigate the environmental and economic issues associated with waste LIBs. In this work, we demonstrate an efficient direct recycling method to regenerate degraded lithium manganese oxide (LMO) cathodes to restore their high capacity, long cycling stability, and high rate performance, on par with pristine LMO materials. This one-step regeneration, achieved by a hydrothermal reaction in dilution Li-containing solution, enables the reconstruction of desired stoichiometry and microphase purity, which is further validated by testing spent LIBs with different states of health. Life-cycle analysis suggested the great environmental and economic benefits enabled by this direct regeneration method compared with today's pyro- and hydrometallurgical processes. This work not only represents a fundamental understanding of the relithiation mechanism of spent cathodes but also provides a potential solution for sustainable and closed-loop recycling and remanufacturing of energy materials.

Spinel-Layered Intergrowth Composite Cathodes for Sodium-Ion Batteries

The vital challenge of a layered manganese oxide cathode for sodium-ion batteries is its severe capacity degradation and sluggish ion diffusion kinetics caused by irreversible phase transitions. In response to this problem, the spinel-layered manganese-based composite with an intergrowth structure is ingeniously designed by virtue of an interesting spinel-to-layered transformation in the delithiated LiMn₂O₄ under Na⁺ insertion. This unique spinel-layered intergrowth structure is strongly confirmed by combining multiple structure analysis techniques. The layered component can provide more reversible capacity, while the spinel component is crucial for the stabilized crystal structure and accelerated ion diffusion kinetics. As an appealing cathode for sodium-ion batteries, the layered-spinel composite delivers a high reversible capacity of 180.9 mAh g^-1, excellent cycling stability, and superior rate capability with 55.7 mAh g^-1 at 12 C. Furthermore, the reaction mechanism upon Na⁺ extraction/insertion is revealed in detail by ex situ X-ray diffraction and X-ray photoelectron spectroscopy, indicating that Na⁺ ions can be accommodated by the layered structure at a low voltage and by the spinel at a high voltage. This study will provide a new idea for the rational design of an advanced cathode for sodium-ion batteries.

Red phosphorus decorated electrospun carbon anodes for high efficiency lithium ion batteries

Electrospinning is a powerful and versatile technique to produce efficient, specifically tailored and high-added value anodes for lithium ion batteries. Indeed, electrospun carbon nanofibers (CNFs) provide faster intercalation kinetics, shorter diffusion paths for ions/electrons transport and a larger number of lithium insertion sites with respect to commonly employed powder materials. With a view to further enhance battery performances, red phosphorous (RP) is considered one of the most promising materials that can be used in association with CNFs. RP/CNFs smart combinations can be exploited to overcome RP low conductivity and large volume expansion during cycling. In this context, we suggest a simple and cost effective double-step procedure to obtain high-capacity CNFs anodes and to enhance their electrochemical performances with the insertion of red phosphorous in the matrix. We propose a simple dropcasting method to confine micro- and nanosized RP particles within electrospun CNFs, thus obtaining a highly efficient, self-standing, binder-free anode. Phosphorous decorated carbon mats are characterized morphologically and tested in lithium ion batteries. Results obtained demonstrate that the reversible specific capacity and the rate capability of the obtained composite anodes is significantly improved with respect to the electrospun carbon mat alone.

Nanoscale Phenomena in Lithium-Ion Batteries

The electrochemical properties and performances of lithium-ion batteries are primarily governed by their constituent electrode materials, whose intrinsic thermodynamic and kinetic properties are understood as the determining factor. As a part of complementing the intrinsic material properties, the strategy of nanosizing has been widely applied to electrodes to improve battery performance. It has been revealed that this not only improves the kinetics of the electrode materials but is also capable of regulating their thermodynamic properties, taking advantage of nanoscale phenomena regarding the changes in redox potential, solid-state solubility of the intercalation compounds, and reaction paths. In addition, the nanosizing of materials has recently enabled the discovery of new energy storage mechanisms, through which unexplored classes of electrodes could be introduced. Herein, we review the nanoscale phenomena discovered or exploited in lithium-ion battery chemistry thus far and discuss their potential implications, providing opportunities to further unveil uncharted electrode materials and chemistries. Finally, we discuss the limitations of the nanoscale phenomena presently employed in battery applications and suggest strategies to overcome these limitations.

Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery

Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn₂O₄ cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn₂O₄ exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn₂O₄ with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.

To unlock the potential of Mn-based cathode materials, the fast capacity fading process has to be first understood. Here the authors utilize advanced characterization techniques to look at a spinel LiMn₂O₄ system, revealing that a combination of irreversible structural transformations and Mn dissolution takes responsibility.

Bioprospecting solid binding polypeptides for lithium ion battery cathode materials

Biotemplating presents a promising approach to improve the performance of inorganic materials via specific control over morphology, crystal structure, and the size of particles during synthesis and assembly. Among other biotemplates, solid binding polypeptides (SBPs) isolated for the material of interest provide high binding affinity and selectivity due to distinct combinations of functional groups found in amino acids. Nanomaterials assembled and synthesized with SBPs have found widespread applications from drug delivery to catalysis and energy storage due to their improved properties. In this study, the authors describe the identification of SBPs for binding to Li-ion battery cathode materials LiCoPO₄, LiMn_1.5Ni_0.5O₄, and LiMn₂O₄, which all have potential for improvement toward their theoretical values. The binding affinity of isolated peptides was assessed via phage binding assays and confirmed with electron microscopy in order to select for potential biotemplates. The authors demonstrate ten binding peptides for each material and analyze the sequences for enrichment in specific amino acids toward each structure (olivine and spinel oxide), as well as the test for specificity of selected sequences. In further studies, the authors believe that the isolated SBPs will serve as a template for synthesis and aid in assembly of cathode materials resulting in improved electrochemical properties for Li-ion batteries.

An all manganese-based oxide nanocrystal cathode and anode for high performance lithium-ion full cells

Manganese oxide nanocrystals are of great interest for producing advanced high-performance lithium ion batteries owing to the shortened lithium ion diffusion length and accelerated interfacial charge transfer rate. Here we have developed a well-controlled generic method to synthesize monodisperse MnO nanocrystals, and present a comparative study regarding the effect of crystallite size on electrochemical stability. Nanocrystalline MnO with a size of about 10 nm shows the optimal lithium-storage performance. Notably, Mn-based nanocrystals retain their stable cyclability and excellent high-rate performance as both the anode and cathode. The all-nanocrystal MnO/C//LMO Li-ion full cells not only significantly improve the electrochemical properties of Mn-based materials but also open up avenues for the future development of various energy devices.

Aqueous Zinc-Ion Storage in MoS2 by Tuning the Intercalation Energy

Aqueous Zn-ion batteries present low-cost, safe, and high-energy battery technology but suffer from the lack of suitable cathode materials because of the sluggish intercalation kinetics associated with the large size of hydrated zinc ions. Herein we report an effective and general strategy to transform inactive intercalation hosts into efficient Zn²⁺ storage materials through intercalation energy tuning. Using MoS₂ as a model system, we show both experimentally and theoretically that even hosts with an originally poor Zn²⁺ diffusivity can allow fast Zn²⁺ diffusion. Through simple interlayer spacing and hydrophilicity engineering that can be experimentally achieved by oxygen incorporation, the Zn²⁺ diffusivity is boosted by 3 orders of magnitude, effectively enabling the otherwise barely active MoS₂ to achieve a high capacity of 232 mAh g^-1, which is 10 times that of its pristine form. The strategy developed in our work can be generally applied for enhancing the ion storage capacity of metal chalcogenides and other layered materials, making them promising cathodes for challenging multivalent ion batteries.

Correlative Electrochemical Microscopy of Li-Ion (De)intercalation at a Series of Individual LiMn2 O4 Particles

The redox activity (Li-ion intercalation/deintercalation) of a series of individual LiMn2 O4 particles of known geometry and (nano)structure, within an array, is determined using a correlative electrochemical microscopy strategy. Cyclic voltammetry (current-voltage curve, I-E) and galvanostatic charge/discharge (voltage-time curve, E-t) are applied at the single particle level, using scanning electrochemical cell microscopy (SECCM), together with co-location scanning electron microscopy that enables the corresponding particle size, morphology, crystallinity, and other factors to be visualized. This study identifies a wide spectrum of activity of nominally similar particles and highlights how subtle changes in particle form can greatly impact electrochemical properties. SECCM is well-suited for assessing single particles and constitutes a combinatorial method that will enable the rational design and optimization of battery electrode materials.

Effect of Passivating Shells on the Chemistry and Electrode Properties of LiMn2O4 Nanocrystal Heterostructures

Building a stable chemical environment at the cathode/electrolyte interface is directly linked to the durability of Li-ion batteries with high energy density. Recently, colloidal chemistry methods have enabled the design of core-shell nanocrystals of Li_{1+ x}Mn_{2- x}O₄, an important battery cathode, with passivating shells rich in Al³⁺ through a colloidal synthetic route. These heterostructures combine the presence of redox-inactive ions on the surface to minimize undesired reactions, with the coverage of each individual particle in an epitaxial manner. Although they improve electrode performance, the exact chemistry and structure of the shell as well as the precise effect of the ratio between the shell and the active core remain to be elucidated. Correlation of these parameters to electrode properties would serve to tailor the heterostructure design toward complete shutdown of undesired reactions. These knowledge gaps are the target of this study. Li_{1+ x}Mn_{2- x}O₄ nanocrystals with Al³⁺-rich shells of different thicknesses were synthesized. Multimodal characterization comprehensively revealed the elemental distribution, electronic state, and crystallinity in the heterostructures, which confirmed the potential of this approach to finely tune passivating layers. All of the modified nanocrystals improved the capacity retention while retaining charge storage compared to the bare counterpart, even under harsh conditions.

Manganese neurotoxicity: nano-oxide compensates for ion-damage in mammals

Here, we have shown that citrate functionalized Mn₃O₄nanoparticles can ameliorate Mn-induced neurotoxicity (Parkinson's-like syndrome) through the chelation of excess Mn ions and subsequent reduction of oxidative damage.

Enhanced Lithium Transport by Control of Crystal Orientation in Spinel LiMn2O4 Thin Film Cathodes

A promising cathode material for rechargeable batteries is LiMn2O4, which exhibits higher operating voltage, reduced toxicity and lower costs as compared to commonly used LiCoO2 cathodes. However, LiMn2O4 suffers from limited cycle life, as excessive capacity fading occurs during battery cycling due to dissolution of Mn into the acidic electrolyte. Here, we show that by structural engineering of stable, epitaxial LiMn2O4 thin films the electrochemical properties can be enhanced as compared to polycrystalline samples. Control of the specific crystal orientation of the LiMn2O4 thin films resulted in dramatic differences in surface morphology with pyramidal, rooftop or flat features for respectively (100), (110), and (111) orientations. All three types of LiMn2O4 films expose predominantly  ⟨111⟩ crystal facets, which is the lowest energy state surface for this spinel structure. The (100)-oriented LiMn2O4 films exhibited the highest capacities and (dis)charging rates up to 33C, and good cyclability over a thousand cycles, demonstrating enhanced cycle life without excessive capacity fading as compared to previous polycrystalline studies.

Crystal structural design of exposed planes: express channels, high-rate capability cathodes for lithium-ion batteries

Developing high-performance lithium ion batteries (LIBs) requires optimization of every battery component. Currently, the main problems lie in the mismatch of electrode capacities, especially the excessively low capacity of cathodes compared with that of anodes. Due to the anisotropy of the crystal structure, different crystal planes play different roles in the transmission of lithium ions. Among these, the {010} facets of layered-structure materials, the (110) planes of spinel cathodes and the (010) planes of olivine cathodes can provide open surface structures, which furnish express channels for the rapid and efficient transmission of lithium ions, leading to enhanced rate performance. However, due to the high-energy surfaces of these crystal planes, they tend to disappear in the synthetic process, forming thermodynamic equilibrium products dominated by low-energy and electrochemically-inactive planes. From the structure design of the material itself, preparing functional materials with specific morphologies and crystal structures is considered to be the most effective way to improve the cyclability and rate performance of LIB cathodes. In this review, we highlight the latest developments in selectively exposing the crystal planes of LIB cathode materials. The synthetic method, the corresponding electrochemical performance, especially the rate capability, and the growth mechanism have been systematically summarized for layered-structure cathodes of LiCoO2, LiNixCoyMn1-x-yO2 and Li2MnO3·LiMO2, spinel cathodes of LiMn2O4 and LiNi0.5Mn1.5O4, and olivine cathodes of LiFePO4. This in-depth discussion and understanding is beneficial for the rational design of well-performing LIB cathodes and can provide direction and perspectives for future work.

Designing High-Performance Nanostructured P2-type Cathode Based on a Template-free Modified Pechini Method for Sodium-Ion Batteries

Layered oxides are promising cathode materials for sodium-ion batteries because of their high theoretical capacities. However, many of these layered materials experience severe capacity decay when operated at high voltage (>4.25 V), hindering their practical application. It is essential to design high-voltage layered cathodes with improved stability for high-energy-density operation. Herein, nano P2-Na_2/3(Mn_0.54Ni_0.13Co_0.13)O₂ (NCM) materials are synthesized using a modified Pechini method as a prospective high-voltage sodium storage component without any modification. The changes in the local ionic state around Ni, Mn, and Co ions with respect to the calcination temperature are recorded using X-ray absorption fine structure analysis. Among the electrodes, NCM fired at 850 °C (NCM-850) exhibits excellent electrochemical properties with an initial capacity and energy density of 148 mAh g^-1 and 555 Wh kg^-1, respectively, when cycled between 2 and 4.5 V at 160 mA g^-1 along with improved cyclic stability after 100 charge/discharge cycles. In addition, the NCM-850 electrode is capable of maintaining a 75 mAh g^-1 capacity even at a current density of 3200 mA g^-1. In contrast, the cell fabricated with NCM obtained at 800 °C shows continuous capacity fading because of the formation of an impurity phase during the synthesis process. The obtained capacity, rate performance, and energy density along with prolonged cyclic life for the cell fabricated with the NCM-850 electrodes are some of the best reported values for sodium-ion batteries as compared to those of other p2-type sodium intercalating materials.

Hierarchically Nanostructured Transition Metal Oxides for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li-ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.

Improving the cycling stability of lithium-sulfur batteries by hollow dual-shell coating

Herein, a novel hybrid S@MnO2@C nanosphere, comprising sulfur nanoparticles encapsulated by a MnO2@C hollow dual-shell, is reported. Benefiting from a conductive C outer layer, the S@MnO2@C hybrid nanosphere provided highly efficient pathways for fast electron/ion transfer and sufficient free space for the expansion of the encapsulated sulfur nanoparticles. Moreover, the dual-shell composed of a MnO2 inner layer and a C outer layer coating on S not only improved the efficacious encapsulation of sulfur, but also significantly suppressed the dissolution of polysulfides during cycling. As a result, the S@MnO2@C electrode shows high capacity, high coulombic efficiency and excellent cycling stability. The S@MnO2@C cathode delivered a discharge capacity of 593 mA h g-1 in the fourth cycle and was able to maintain 573 mA h g-1 after 100 charge-discharge cycles at 1.0C, corresponding to a capacity retention of 96.6%.

Complimentary effects of annealing temperature on optimal tuning of functionalized carbon–V2O5 hybrid nanobelts for targeted dual applications in electrochromic and supercapacitor devices

Herein, carbon nanosphere-decorated vanadium pentoxide (C@V₂O₅) hybrid nanobelts were grown via a single step hydrothermal route with improved electronic conductivity as compared to that of pristine oxide. This hybrid nanomaterial exhibits different complimentary ranges of optimum post-growth annealing temperatures, which are suitable for dual applications either in electro-chromic smart windows or in supercapacitors. C@V₂O₅ nanobelts annealed at 350 °C appear to favor electro-chromic applications. They exhibit maximum dynamic optical transmission modulation as they switch from yellow to dark green, fast switching response, and high visible transmittance. In contrast, C@V₂O₅nanobelts annealed at 250 °C have been found to be most suitable for supercapacitor applications. They display a high specific capacity and an enhanced diffusion coefficient. Moreover, they exhibit long lifetimes with a capacity retention of ∼94% even after 5000 cycles of operation. Therefore, the obtained results clearly indicate that optimization of the post-growth annealing temperatures is very important and rather complementary in nature in terms of determining the most favorable device functionalities. It enables us to optimally tune these hybrid nanomaterials for targeted, device-specific, energy applications in either electrochromic or supercapacitor technologies simply based on the annealing temperature alone.

Herein, carbon nanosphere-decorated vanadium pentoxide (C@V₂O₅) hybrid nanobelts were grown via a single step hydrothermal route with improved electronic conductivity as compared to that of pristine oxide.

The nanoscale circuitry of battery electrodes

Developing high-performance, affordable, and durable batteries is one of the decisive technological tasks of our generation. Here, we review recent progress in understanding how to optimally arrange the various necessary phases to form the nanoscale structure of a battery electrode. The discussion begins with design principles for optimizing electrode kinetics based on the transport parameters and dimensionality of the phases involved. These principles are then used to review and classify various nanostructured architectures that have been synthesized. Connections are drawn to the necessary fabrication methods, and results from in operando experiments are highlighted that give insight into how electrodes evolve during battery cycling.

Novel Approach for in Situ Recovery of Lithium Carbonate from Spent Lithium Ion Batteries Using Vacuum Metallurgy

Lithium is a rare metal because of geographical scarcity and technical barrier. Recycling lithium resource from spent lithium ion batteries (LIBs) is significant for lithium deficiency and environmental protection. A novel approach for recycling lithium element as Li₂CO₃ from spent LIBs is proposed. First, the electrode materials preobtained by mechanical separation are pyrolyzed under enclosed vacuum condition. During this process the Li is released as Li₂CO₃ from the crystal structure of lithium transition metal oxides due to the collapse of the oxygen framework. An optimal Li recovery rate of 81.90% is achieved at 973 K for 30 min with a solid-to-liquid ratio of 25 g L^-1, and the purity rate of Li₂CO₃ is 99.7%. The collapsed mechanism is then presented to explain the release of lithium element during the vacuum pyrolysis. Three types of spent LIBs including LiMn₂O₄, LiCoO₂, and LiCo_xMn_yNi_zO₂ are processed to prove the validity of in situ recycling Li₂CO₃ from spent LIBs under enclosed vacuum condition. Finally, an economic assessment is taken to prove that this recycling process is positive.

High Performance Poly(viologen)-Graphene Nanocomposite Battery Materials with Puff Paste Architecture

Four linear poly(viologens) (PV1, PV2: phenylic, PV3: benzylic, and PV4: aliphatic) in tight molecular contact with reduced graphene oxide (rGO), that is, PV@rGO, were prepared and used as anodic battery materials. These composites show exceptionally high, areal, volumetric, and current densities, for example, PV1@rGO composites (with 15 wt % rGO, corresponding to 137 mAh g^-1) show 13.3 mAh cm^-2 at 460 μm and 288 mAh cm^-3 with 98% Coulombic efficiency at current densities up to 1000 A g^-1, better than any reported organic materials. These remarkable performances are based on (i) molecular self-assembling of PVs on individual GO sheets yielding colloidal PV@GO and (ii) efficient GO/rGO transformation electrocatalyzed by PVs. Ion breathing during charging/discharging was studied by electrochemical quartz crystal microbalance and electrochemical atomic force microscopy revealing an absolute reversible and strongly anisotropic thickness oscillation of PV1@rGO at a right angle to the macroscopic current collector. It is proposed that such stress-free breathing is the key property for good cyclability of the battery material. The anisotropy is related to a puff paste architecture of rGO sheets parallel to the macroscopic current collector. A thin graphite sheet electrode with an areal capacity of 1.23 mAh cm^-2 is stable over 200 bending cycles, making the material applicable for wearable electronics. The polymer acts as a lubricant between the rGO layers if shearing forces are active.

Recycling metals from lithium ion battery by mechanical separation and vacuum metallurgy

The large-batch application of lithium ion batteries leads to the mass production of spent batteries. So the enhancement of disposal ability of spent lithium ion batteries is becoming very urgent. This study proposes an integrated process to handle bulk spent lithium manganese (LiMn₂O₄) batteries to in situ recycle high value-added products without any additives. By mechanical separation, the mixed electrode materials mainly including binder, graphite and LiMn₂O₄ are firstly obtained from spent batteries. Then, the reaction characteristics for the oxygen-free roasting of mixed electrode materials are analyzed. And the results show that mixed electrode materials can be in situ converted into manganese oxide (MnO) and lithium carbonate (Li₂CO₃) at 1073K for 45min. In this process, the binder is evaporated and decomposed into gaseous products which can be collected to avoid disposal cost. Finally, 91.30% of Li resource as Li₂CO₃ is leached from roasted powders by water and then high value-added Li₂CO₃ crystals are further gained by evaporating the filter liquid. The filter residues are burned in air to remove the graphite and the final residues as manganous-manganic oxide (Mn₃O₄) is obtained.

Low-Temperature Carbon Coating of Nanosized Li1.015Al0.06Mn1.925O4 and High-Density Electrode for High-Power Li-Ion Batteries

Despite their good intrinsic rate capability, nanosized spinel cathode materials cannot fulfill the requirement of high electrode density and volumetric energy density. Standard carbon coating cannot be applied on spinel materials due to the formation of oxygen defects during the high-temperature annealing process. To overcome these problems, here we present a composite material consisting of agglomerated nanosized primary particles and well-dispersed acid-treated Super P carbon black powders, processed below 300 °C. In this structure, primary particles provide fast lithium ion diffusion in solid state due to nanosized diffusion distance. Furthermore, uniformly dispersed acid-treated Super P (ASP) in secondary particle facilitates lower charge transfer resistance and better percolation of electron. The ASPLMO material shows superior rate capability, delivering 101 mAh g^-1 at 300 C-rate at 24 °C, and 75 mAh g^-1 at 100 C-rate at -10 °C. Even after 5000 cycles, 86 mAh g^-1 can be achieved at 30 C-rate at 24 °C, demonstrating very competitive full-cell performance.