High-performance Cathode Materials Research Articles

Anionic-surfactant-assisted synthesis of Ni0.8Co0.1Mn0.1(OH)2 as precursors of high-performance cathode materials for lithium-ion batteries

Anionic-surfactant-assisted synthesis of Ni0.8Co0.1Mn0.1(OH)2 as precursors of high-performance cathode materials for lithium-ion batteries

In Situ Surface Reaction for the Preparation of High-Performance Li-Rich Mn-Based Cathode Materials with Integrated Surface Functionalization.

Li-rich Mn-based cathode materials (LLOs) are often faced with problems such as low initial Coulombic efficiency (ICE), limited rate performance, voltage decay, and structural instability. Addressing these problems with a single approach is challenging. To overcome these limitations, we developed an LLO with surface functionalization using a simple fabrication method. This two-step process involved a liquid-stage NaBF4 treatment followed by an in situ chemical reaction during sintering. This reaction led to the creation of oxygen vacancies (OV), spinel structures, and doping with Na at the Li site, B at the tetrahedral interstitial spaces of O in both the transition-metal (TM) layer and Li layers as well as the octahedral interstices in the TM layer, and F at the O site. We have carried out a thorough study and employed density functional theory calculations to reveal the hidden mechanisms. The treatment not only increases the electrical conductivity but also changes the oxygen charge environment and inhibits lattice oxygen activity. Surprisingly, the B-O bond is so strong that it prevents the migration of TM within the tetrahedral interstitial spaces of O in both the TM and Li layers, hence stabilizing its structure. This bonding interaction strengthens the transition of the TM 3d and O 2p states to lower energy levels, thus causing an increase in the redox potentials. Hence, a rise in the operating voltage occurs. Of special importance, this therapy dramatically increases the ICE to 90.29% and keeps a specified capacity of 203.3 mAh/g after 100 cycles at 1C, which is an excellent capacity retention of 89.94%. This study introduces ideas and methods to tackle the challenges associated with LLOs in batteries. It also provides compelling evidence for the development of high-energy-density Li-ion batteries.

Sulfurized Two-Dimensional Conductive Metal-Organic Framework as a High-Performance Cathode Material for Rechargeable Mg Batteries.

Rechargeable Mg batteries are a promising energy storage technology to overcome the limitations inherent to Li ion batteries. A critical challenge in advancing Mg batteries is the lack of suitable cathode materials. In this work, we report a cathode design that incorporates S functionality into two-dimensional metal-organic-frameworks (2D-MOFs). This new cathode material enables good Mg2+ storage capacity and outstanding cyclability. It was found that upon the initial Mg2+ insertion and disinsertion, there is an apparent structural transformation that crumbles the layered 2D framework, leading to amorphization. The resulting material serves as the active material to host Mg2+ through reduction and/or oxidation of S and, to a limited extent, O. The reversible nature of S and O redox chemistry was confirmed by spectroscopic characterizations and validated by density functional calculations. Importantly, during the Mg2+ insertion and disinsertion process, the 2D nature of the framework was maintained, which plays a key role in enabling the high reversibility of the MOF cathode.

Regulating electronic structure of anionic oxygen by Ti4+ doping to stabilize layered Li-rich oxide cathodes for Li-ion batteries

Abstract Layered Li-rich oxide cathodes enable to activate lattice oxygen anions redox in the charge compensation process and provide superior high specific capacity over 250 mAh/g due to their unique configuration, and thus attracting great attentions as promising cathode candidates for Li-ion batteries. However, how to better stabilize the bulk lattice oxygen framework and surface structure, and slow down the release of oxygen, is still major bottleneck to develop high performance Li-rich materials. Transition metal ions with outer d0 electronic configuration have distortable configuration, which can accommodate the local structure and chemical environment of the material, and then improve structural stability. Herein this work, the d0 transition metal Ti4+ is used as doping element to improve the chemical and structural stability, capacity retention and lithium ion diffusion kinetics of Li-rich material. The role of Ti in the material modification is revealed through synchrotron-based soft X-ray absorption spectroscopy, XRD, XPS and electrochemical tests. The improvement in structural stability can be attributed to that Ti doping can adjust the hybridization of O2p and TM3d to regulate the local electronic structure of both bulk lattice oxygen and surface oxygen vacancies. It is hoped that this work should shed light on the development of high-performance cathode materials for Li-ion Batteries.

Lithiophilic Dibenzamide Linkages to Impart Lithium Storage Capacity in Porous Polybenzamides.

Polymer-based organic cathode materials have shown immense promise for lithium storage, owing to their structural diversity and functional group tunability. However, designing appropriate high-performance cathode materials with a high-rate capability and long cycle life remains a significant challenge. It is quintessential to design polymer-based electrodes with lithiophilic linkages. Herein, we design a bifurcated dibenzamide (DBA) linkage having lithiophilic functionalities. 1H NMR has been used as an experimental tool to understand the lithiophilic nature of the DBAs. Considering the strong Li+ affinity of DBAs, a series of polybenzamides have been designed as lithium storage systems. The design of porous polybenzamides consists of amides as only redox-active functionalities, and the rest are inactive phenyl units. Porous polybenzamides, when tested as cathodes against a Li-metal anode, displayed high capacity and rate performance, demonstrating their redox activity. The most efficient polybenzamide (TAm-TA) delivered a specific capacity of 248 mA h g-1 at 1C. TAm-TA retained 63% of its specific capacity at a very high rate of 10C (157 mA h g-1). Notably, polybenzamides displayed a capacity enhancement during long cycling, tending to achieve their theoretical capacity. Long cycling stability tests over 3000 cycles at a rate of 1.3C and over 6000 cycles at elevated rates (5C to 40C) demonstrate the electrochemical robustness of dibenzamide linkages. Finally, two full-cell experiments using TAm-TA as both cathode and anode were conducted, which delivered high capacity, demonstrating that TAm-TA is a promising candidate for Li+-ion batteries (LIBs). Furthermore, the ex situ Fourier transform infrared (FT-IR), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) studies revealed the stepwise lithiation/delithiation mechanism for polybenzamides.

Tightly confined tellurium nanocrystals in few-layer expanded graphite with Te–C bonds toward highly reversible zinc storage

Tellurium (Te) has great potential as high-performance cathode materials for aqueous zinc-ion batteries (AZIBs) owing to high electronic conductivity and volumetric capacity. Nevertheless, its poor utilization and large volume expansion result in insufficient rate and cycle performances, thereby, impeding practical application. Herein, a kind of Te/carbon composite was prepared via a ball-milling method, in which Te nanocrystals were tightly confined in few-layer expanded graphite (EG) with Te–C bonds (denoted as Te@EG). In addition to maintaining structural stability, such unique nanocomposite shows abundant electrochemically active sites and efficient charge transfer channels, which is beneficial to the utilization of Te. More importantly, the Te–C bonds between Te nanocrystals and EG can enhance the adsorption of Zn2+ and reduce the Zn2+ migration barrier, which contributes to promoting electrochemical kinetics. Consequently, the Te@EG cathode for the AZIBs exhibits sufficient specific capacity (412 mAh g–1 at 0.1 A g–1), high-rate performance (284 mAh g–1 at 3 A g–1), and reliable cycling stability (94% capacity retention at 1 A g–1 after 500 cycles). Furthermore, the soft-packaged Zn//Te@EG battery delivers excellent flexibility and cycling stability. This study offers a perspective on rational design of Te-based cathodes for practical AZIBs.

The enhancement and impact of Se doping on the electrochemical properties of LiMn2O4 cathode material for aqueous Li-ion batteries

Spinel LiMn2O4 is a promising cathode material for lithium-ion batteries. However, due to the Jahn-Teller effect and Mn dissolution, its capacity decreases seriously in the cycle process, which hinders its wider application. In the course of our research, we discovered that a modest infusion of Se-doping is capable of significantly augmenting the oxygen vacancy within the material, improve the conductivity of the LiMn2O4 material and promotes superior battery performance. Moreover, due to Se-doped the average valence state of Mn is raised, which effectively mitigates the Jahn-Teller effect. The optimized sample exhibits high capacity, long cycle life, and superior rate capability, with an initial discharge specific capacity of 101.0 mAh·g−1 at 7 C and capacity retention of 87.3 % after 200 cycles. The maximum specific discharge capacity of the full battery during the cycle was 97.9 mAh·g−1, the capacity retention rate after 200 cycles was 78.2 %, and the maximum energy density during the cycle is 145.1 Wh·Kg−1, which was nearly twice that of the single lithium-ion battery in this paper. The effect of Se-doped on the properties of LiMn2O4 cathode materials provides a new idea for the development of high-performance spinel lithium manganese oxide cathode materials.

High performance rechargeable aluminium ion batteries enabled by full utilization and understanding of polyaniline cathodes

As a renowned conductive polymer, polyaniline (PANI) shows remarkable potential in organic cathode materials for rechargeable aluminium ion batteries (RAIBs). However, existing research has not given sufficient understanding and explanation of the structure and states of PANI but failed to achieve ideal electrochemical performance. In this study, we differentiate and investigate for the first time its primary-doped (PANI-1), re-doped (PANI-Re), secondary-doped (PANI-2), and emeraldine based (PANI-EB) forms, meanwhile attempt to enhance the conductivity of PANI-EB using multi-walled carbon nanotubes (PANI-EB@C). Among them, the high-doped PANI-2 and non-doped PANI-EB exhibit theoretical capacity utilization far superior to lower doped PANI-1 and PANI-Re, with both specific capacities reaching approximately 225 mAh/g (full capacity utilization rate of 76.53 %) at a current density of 1 A/g, while maintaining capacity retention rates of 92.89 % after 2000 cycles and 92.44 % after 5000 cycles, respectively. Furthermore, the high-conductivity PANI-EB@C displays a discharge specific capacity of 284 mAh/g (full capacity utilization rate of 96.59 %), with a capacity retention rate of 91.19 % after 5000 cycles. Electrochemical analysis, Gaussian theoretical calculations, ex-situ characterization collectively indicate that the electrochemical performance of doped PANI is positively correlated with the degree of doping-induced conductivity changes, while the unique internal redox process of PANI-EB enhances the release of performance and could be further optimized by the assistant of conductivity medium. This work advances the classification of the electrochemical performance and structural understanding of PANI cathode materials to an extremely high stage, towards the practical application of a low-cost, high-performance, sustainable, and green cathode material in large-scale energy storage devices.

Sodium layered oxide cathodes: properties, practicality and prospects.

Rechargeable sodium-ion batteries (SIBs) have emerged as an advanced electrochemical energy storage technology with potential to alleviate the dependence on lithium resources. Similar to Li-ion batteries, the cathode materials play a decisive role in the cost and energy output of SIBs. Among various cathode materials, Na layered transition-metal (TM) oxides have become an appealing choice owing to their facile synthesis, high Na storage capacity/voltage that are suitable for use in high-energy SIBs, and high adaptivity to the large-scale manufacture of Li layered oxide analogues. However, going from the lab to the market, the practical use of Na layered oxide cathodes is limited by the ambiguous understanding of the fundamental structure-performance correlation of cathode materials and lack of customized material design strategies to meet the diverse demands in practical storage applications. In this review, we attempt to clarify the fundamental misunderstandings by elaborating the correlations between the electron configuration of the critical capacity-contributing elements (e.g., TM cations and oxygen anion) in oxides and their influence on the Na (de)intercalation (electro)chemistry and storage properties of the cathode. Subsequently, we discuss the issues that hinder the practical use of layered oxide cathodes, their origins and the corresponding strategies to address their issues and accelerate the target-oriented research and development of cathode materials. Finally, we discuss several new Na layered cathode materials that show prospects for next-generation SIBs, including layered oxides with anion redox and high entropy and highlight the use of layered oxides as cathodes for solid-state SIBs with higher energy and safety. In summary, we aim to offer insights into the rational design of high-performance Na layered oxide cathode materials towards the practical realization of sustainable electrochemical energy storage at a low cost.

An Active Strategy to Reduce Residual Alkali for High-Performance Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Residual alkali is one of the biggest challenges for the commercialization of sodium-based layered transition metal oxide cathode materials since it can even inevitably appear during the production process. Herein, taking O3-type Na0.9Ni0.25Mn0.4Fe0.2Mg0.1Ti0.05O2 as an example, an active strategy is proposed to reduce residual alkali by slowing the cooling rate, which can be achieved in one-step preparation method. It is suggested that slow cooling can significantly enhance the internal uniformity of the material, facilitating the reintegration of Na+ into the bulk material during the calcination cooling phase, therefore substantially reducing residual alkali. The strategy can remarkably suppress the slurry gelation and gas evolution and enhance the structural stability. Compared to naturally cooled cathode materials, the capacity retention of the slowly cooled electrode material increases from 76.2% to 85.7% after 300 cycles at 1C. This work offers a versatile approach to the development of advanced cathode materials toward practical applications.

Porous CuO Microspheres as Long-Lifespan Cathode Materials for Aqueous Zinc-Ion Batteries.

Cathode materials with conversion mechanisms for aqueous zinc-ion batteries (AZIBs) have shown a great potential as next-generation energy storage materials due to their high discharge capacity and high energy density. However, improving their cycling stability has been the biggest challenge plaguing researchers. In this study, CuO microspheres were prepared using a simple hydrothermal reaction, and the morphology and crystallinity of the samples were modulated by controlling the hydrothermal reaction time. The as-synthesized materials were used as cathode materials for AZIBs. The electrochemical experiments showed that the CuO-4h sample, undergoing a hydrothermal reaction for 4 h, had the longest lifecycle and the best rate of capability. A discharge capacity of 131.7 mAh g-1 was still available after 700 cycles at a current density of 500 mA g-1. At a high current density of 1.5 A g-1, the maintained capacity of the cell is 85.4 mA h g-1. The structural evolutions and valence changes in the CuO-4h cathode material were carefully explored by using ex situ XRD and ex situ XPS. CuO was reduced to Cu2O and Cu after the initial discharge, and Cu was oxidized to Cu2O instead of CuO during subsequent charging processes. We believe that these findings could introduce a novel approach to exploring high-performance cathode materials for AZIBs.

CNT Composite β-MnO2 with Fiber Cable Shape as Cathode Materials for Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (AZIBs) have developed into one of the most attractive materials for large-scale energy storage owing to their advantages such as high energy density, low cost, and environmental friendliness. Nevertheless, the sluggish diffusion kinetics and inherent impoverished conductivity affect their practical application. Herein, the β-MnO2 composited with carbon nanotubes (CNT@M) is prepared through a simple hydrothermal approach as a high-performance cathode for AZIBs. The CNT@M electrode exhibits excellent cycling stability, in which the maximum specific discharge capacity is 259 mA h g-1 at 3 A g-1, and there is still 220 mA h g-1 after 2000 cycles. The specific capacity is obviously better than that of β-MnO2 (32 mA h g-1 after 2000 cycles). The outstanding electrochemical performance of the battery is inseparable from the structural framework of CNT and inherent high conductivity. Furthermore, CNT@M can form a complex conductive network based on CNTs to provide excellent ion diffusion and charge transfer. Therefore, the active material can maintain a long-term cycle and achieve stable capacity retention. This research provides a reasonable solution for the reliable conception of Mn-based electrodes and indicates its potential application in high-performance AZIB cathode materials.

Boosting proton intercalation via sulfur anion doping in V2O3 cathode materials towards high capacity and rate performance of aqueous zinc ion batteries

Aqueous zinc-ion batteries (ZIBs) are a prospective solution for grid-scale energy storage. V2O3 has emerged as a promising cathode candidate with reversible two-electron redox capability for ZIBs. However, it still faces problems such as poor electronic conductivity and sluggish ion embedding kinetics. Herein, we report sulfur anion-doped V2O3 with tunneled structure based on a facile carbothermal reduction method, which can exhibit the significant impact of sulfur anion-doping on proton storage in vanadium-based cathode materials for high capacity and rate performance of ZIBs. The covalent bonds in S-V-O lead to accelerated charge transfer and elevated electronic conductivity. In-situ X-ray diffraction, synchrotron-based X-ray absorption spectroscopy combined with DFT calculations demonstrate that S doping effectively diminishes the adsorption and embedding energies of H+ in V2O3 and greatly boosts proton insertion kinetics. The co-intercalation of H+/Zn2+ helps compensate for the deficiency of Zn2+ insertion/extraction kinetics. Amorphous transition of crystalline V2O3 initiated from initial charging is conducive to mitigating stress and retaining stable cycling capacity. The typical sulfur-doped V2O3 achieves remarkable capacity (470.4 mAh·g−1 at 0.5 A·g−1), excellent rate capability (264.6 mAh·g−1 at 10 A·g−1) and stable long-term cyclability (231.2 mAh·g−1 at 10 A·g−1 after 2000 cycles). Furthermore, the corresponding pouch cells can deliver 26 mAh at 1 A·g−1 after 250 cycles, holding great potential for practical applications.

Ammonium vanadate doped by transition bivalent metal ions for high-performance zinc-ion batteries

Vanadium-based materials are considered as promising cathode materials in aqueous zinc-ion (Zn2+) batteries (AZIBs) because of their abundant valence states and adjustable ion diffusion channels. However, the slow kinetics of the Zn2+ intercalation and the instability of the layered structure during long cycle are the bottlenecks restricting their further development. In this paper, the transition bivalent manganese ions (Mn2+) are introduced into ammonium vanadate (NH4V4O10) to partly replace the NH4+ ions to prepare a high-performance AZIB cathode. After doping transition bivalent Mn2+, the interlayer spacing of NH4V4O10 is enlarged, providing a broadened channel for the diffusion of Zn2+ accordingly. The results reveal that the electrode with the optimal doping quantity has a very high discharge capacity (539.4 mAh/g at 0.2 A/g) and excellent cyclic stability (85.3 % retention of the initial capacity after 3000 cycles at 5 A/g). A highly competitive energy density of 378 Wh kg−1 at 362 W kg−1 is delivered by the corresponding AZIB. Moreover, this method is a general and effective strategy for developing high-performance AZIB cathode materials, as demonstrated by the consistent crystal structure and stable cycling properties for NH4V4O10 doped with other transition bivalent metal cations

Leveraging doping strategies and interface engineering to enhance catalytic transformation of lithium polysulfides for high-performance lithium-sulfur batteries

The commercialization of lithium-sulfur (Li–S) batteries has faced challenges due to the shuttle effect of soluble intermediate polysulfides and the sluggish kinetics of sulfur redox reactions. In this study, a synergistic catalyst medium was developed as a high-performance sulfur cathode material for Li–S batteries. Termed A/R-TiO2@ Ni-N-MXene, this sulfur cathode material features an in-situ derived anatase–rutile homojunction of TiO2 nanoparticles on Ni-N dual-atom-doped MXene nanosheets. Using in-situ transmission electron microscopy (TEM) technique, we observed the growth process of the homojunction for the first time confirming that homojunctions facilitated charge transfer, while dual-atom doping offered abundant active sites for anchoring and converting soluble polysulfides. Theoretical calculations and experiments showed that these synergistic effects effectively mitigated the shuttle effect, leading to improved cycling performance of Li–S batteries. After 500 cycles at a 1C rate, Li–S batteries using A/R-TiO2@Ni-N-MXene as cathode materials exhibited stable and highly reversible capacity with a capacity decay of only 0.056 % per cycle. Even after 150 cycles at a 0.1C rate, a high-capacity retention rate of 62.8 % was achieved. Additionally, efficient sulfur utilization was observed, with 1280.76 mA h/g at 0.1C, 694.24 mA h/g at 1C, alongside a sulfur loading of 1.5–2 mg/cm2. The effective strategy based on homojunctions showcases promise for designing high-performance Li–S batteries.

Preparation of Na+ preintercalated V2O5·nH2O nanobelts with abundant oxygen vacancies as a high-performance cathode material for aqueous zinc-ion batteries

Preparation of Na+ preintercalated V2O5·nH2O nanobelts with abundant oxygen vacancies as a high-performance cathode material for aqueous zinc-ion batteries

Highly reversible transition metal migration in superstructure-free Li-rich oxide boosting voltage stability and redox symmetry

The further practical applications of Li-rich layered oxides are impeded by voltage decay and redox asymmetry, which are closely related to the structural degradation involving irreversible transition metal migration. It has been demonstrated that the superstructure ordering in O2-type materials can effectively suppress voltage decay and redox asymmetry. Herein, we elucidate that the absence of this superstructure ordering arrangement in a Ru-based O2-type oxide can still facilitate the highly reversible transition metal migration. We certify that Ru in superstructure-free O2-type structure can unlock a quite different migration path from Mn in mostly studied cases. The highly reversible migration of Ru helps the cathode maintain the structural robustness, thus realizing terrific capacity retention with neglectable voltage decay and inhibited oxygen redox asymmetry. We untie the knot that the absence of superstructure ordering fails to enable a high-performance Li-rich layered oxide cathode material with suppressed voltage decay and redox asymmetry.

Construction of a bi-continuous charge transport network towards high-performance vanadium-based phosphate cathode materials for potassium ion batteries

As one class of most promising cathode materials for potassium ion batteries (KIBs), polyanionic compounds still suffer from unsatisfactory effective capacity and rate performance due to their poor intrinsic electronic conductivity. In this paper, nanoscale K3V3(PO4)4 (KVP) particles with a bi-continuous charge transport network (denote as KVP-S) are designed and prepared. Carbon nanotubes (CNTs) play a crucial role in this design, not only effectively inhibiting the aggregation and growth of particles, but also providing a three-dimensional (3D) electron conductive network. Benefiting from the advantages of nanoscale particle size and bi-continuous charge transport network, the KVP-S electrode exhibits a high capacity (118mAh g−1 at 20 mA g−1), outstanding rate performance (102 mAh g−1 at 0.5 C; 66 mAh g−1 at 5 C) and excellent cycling stability (94 % retention after 50 cycles at 1 C). Even at a higher rate of 5 C, it still maintains a high capacity retention of 92 % after 300 cycles. More importantly, the capacity can maintain 80 mAh g−1 at 1 C when the mass loading is extended to 4 mg cm−2, In addition, in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) analyses reveal that the potassium storage mechanism of KVP-S is two single-phase solid solution reactions, involving V2+/V3+/V4+ three-electron redox conversions with a total volume change of 5.5 %. This study provides a new way to rationally design nanoscale particle electrodes with highly conductive charge transport networks.

Hydrophobic Two-Dimensional Layered Superstructure of a Polyoxometalate Cluster as the Cathode Material for Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries hold promise for sustainable energy storage, yet challenges in finding high-performance cathode materials persist. Polyoxovanadates (POVs) are emerging as potential candidates due to their structural diversity and robust redox activity. Despite their potential, issues like dissolution in electrolytes, structural degradation, and byproduct accumulation persist. This work introduces a POV-based hydrophobic two-dimensional (2D) layered superstructure that addresses these challenges. The hydrophobic nature minimizes POV dissolution, enhancing structural stability and inhibiting phase transitions during cycling. The 2D arrangement ensures a larger surface area and improved electronic conductivity, resulting in faster kinetics and higher specific capacity. The superstructure demonstrates improved cycle life and an increased operating voltage, marking a significant advancement in POV-based cathode materials for aqueous zinc-ion batteries.

Laser-Scribed Battery Electrodes for Ultrafast Zinc-Ion Energy Storage.

Aqueous Zn batteries are promising for large-scale energy storage applications but are plagued by the lack of high-performance cathode materials that enable high specific capacity, ultrafast charging, and outstanding cycling stability. In this work, we design a laser-scribed nano-vanadium oxide (LNVO) cathode that can simultaneously achieve these properties. Our material stores charge through Faradaic redox reactions on/near the surface at fast rates owing to the small grain size (2-6nm) of vanadium oxide and interpenetrating three-dimensional (3D) graphene network, displaying a surface-controlled capacity contribution (90%-98%). Multiple characterization techniques unambiguously reveal that zinc and hydronium ions co-insert with minimal LNVO lattice change upon cycling. As a result, we demonstrate that a high specific capacity of 553 mAh g-1 can be achieved by the LNVO/Zn system at 0.1 A g-1 , and an impressive 264 mAh g-1 capacity can be retained at 100 A g-1 with a 10 s charge/discharge cycle, showing excellent rate capability. The LNVO/Zn is also capable of reaching >90% capacity retention after 3,000 cycles at a high rate of 30 A g-1, as well as achieving both high energy (369Wh kg-1) and power densities (56,306W kg-1). Moreover, the LNVO cathode retains its excellent cycling performance when integrated into quasi-solid-state pouch cells, further demonstrating mechanical stability and its potential for practical application in wearable and grid-scale applications. This article is protected by copyright. All rights reserved.