Electrochemical Performance Of Electrode Materials Research Articles

Soft-template assisted morphology tuning of NiMoO4 for hybrid supercapacitors

The electrochemical performance of electrode materials depends on various physicochemical properties like particle size, morphology, porosity, etc. of materials. Herewith, a facile surfactant assisted hydrothermal route using cetyltrimethylammonium bromide (CTAB) and hexamethylenetetramine (HMT) is used to successfully synthesize nanostructured nickel molybdate (NiMoO4) with various morphologies. It is found that NiMoO4 possesses different morphologies when synthesized by using these surfactants. With change in morphology, there is a significant increase in diffusion coefficient for sample synthesized with CTAB. It is interesting to note that NiMoO4 synthesized by using CTAB exhibit a high specific capacitance of 947 F g−1 when cycled at 1 A g−1 in 1 M KOH solution as compared to that of 322 F g−1 (synthesized without CTAB), which can be ascribed to its flower-like shape with uniform porosity. Both Ni2+/Ni3+ and Mo6+/Mo4+ redox couples are involved in the capacitive characteristic of NiMoO4, as found from the XPS study. Additionally, a hybrid supercapacitor has been assembled using NiMoO4 as positive electrode and reduced grapgene oxide (rGO) as negative electrode, which can exhibit 107 F g−1 with an operating voltage of 1.6 V with excellent cycling stability of maintaining 94 % capacitance retention after 6000 cycles in 1 M KOH solution. The hybrid supercapacitor can possess an energy density of 37.7 Wh kg−1 and a power density of 8 kW kg−1. Thus, this study enables the importance of tuning the morphology to enhance the capacitance property of transition metal oxide based electrode materials for supercapacitor applications.

Combined Ce-doping and electrochemical activation strategies for boosting the supercapacitance of NiCoO

Heteroatom doping and electrochemical activation have been reported to improve electrochemical performance of electrode materials. However, there is no report about the combination of these two methods to enhance the electrochemical performance of NiCo-oxides. Herein, Ce-doped NiCoO nanocones are grown on porous nickel foam, and electrochemical activation tactic is utilized to further boost the electrochemical performance. Through adjusting the Ce-doping dosage, the optimized NiCoCe-0.25 sample presents the highest capacitance of 1800 F g−1, greatly higher than that of pristine NiCoO (969.4 F g−1). The optimized NiCoCe-0.25 is selected as initial electrode for seeking the best activation condition. The activation process in KOH electrolyte triggers the formation of nanosheets on the surface of nanocones, followed by the growing of thin nanosheets. Therefore, the activation mechanism of Ce-doped NiCoO involves the generation and growing of nanosheets, accompanied by the composition transition from oxides to hydroxides/oxyhydroxides. When lasted for 430 CV cycles, the activation product delivers the maximum capacitance of 3795.8 F g−1 (1897.9 C g−1) at 1 A g−1. The superior performance is attributed to the interconnected framework structure consisted of nanosheets and nanoparticles, as well as the optimized composition. When utilized as positive electrode in a supercapacitor device, Ce-doped NiCoO electrode exhibits a high specific capacitance, cycling stability, and energy density. Therefore, Ce-doping and electrochemical activation tactic can be integrated for enhancing the supercapacitance performance of metal oxides.

Rapid and easy preparation of self-supporting La-mixed NiMoO4 nanofloral materials and their capacitance properties

Rare earth element doped bimetallic oxides are a new technology for improving the electrochemical performance of electrode materials. This article successfully prepared 0.5% La-NiMoO4 flower-like structured nanomaterials directly grown on nickel-based...

Preparation and Electrochemical Performance of Na2-xLixFePO4F/C Composite Cathode Materials with Different Lithium/Sodium Ratios.

With their advantages of abundant raw material reserves, safety, and low toxicity and cost, sodium-ion batteries (SIBs) have gained increasing attention in recent years. Thanks to a high theoretical specific capacity (124 mAh g-1), a high operating voltage (about 3.2 V), and a very stable three-dimensional layered structure, sodium ferric fluorophosphate (Na2FePO4F, NFPF) has emerged as a strong candidate to be used as a cathode material for SIBs. However, applications are currently limited due to the low electronic conductivity and slow ion diffusion rate of NFPF, which result in a low actual specific capacity and a high rate performance. In this study, the authors used a high-temperature solid-phase technique to produce Na2-xLixFePO4F/C (0 ≤ x ≤ 2) and evaluated the impact on electrode performance of materials with different Na+ and Li+ contents (values of x). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were also used to analyze the material's crystal structure and nanostructure. The results show that the material had the best room-temperature performance when x = 0.5. At a charge-discharge rate of 0.1 C, the first discharge-specific capacity of the resulting Na1.5Li0.5FePO4F/C cathode material was 122.9 mAh g-1 (the theoretical capacity was 124 mAh g-1), and after 100 cycles, it remained at 118 mAh g-1, representing a capacity retention rate of 96.2% and a Coulomb efficiency of 98%. The findings of this study demonstrate that combining lithium and sodium ions improves the electrochemical performance of electrode materials.

Cerium-assembled tungsten oxide composite fibers: Adhesive-free electrodes for high performance asymmetric supercapacitors

In this study, in-situ cerium-assembled tungsten oxide carbon nanofibers were successfully prepared via simple electrospinning and calcination technology and were used as flexible electrodes without conductive agent and adhesive. It was confirmed that the introduction of Ce has better maintained the continuous morphology of one-dimensional fibers to provide a continuous uninterrupted reaction position by the SEM TEM and XPS results. The addition of cerium improved the wettability of the material, which was propitious to the penetration of the electrolyte, made the electrolyte more fully contact with the active site, and enhanced the interface transmission effectiveness by the liquid contact angle test. Otherwise, the XRD and XPS results exhibited that the addition of cerium has caused the lattice expansion of the tungsten oxide, which generated the self-adjustable strain relaxation ability of electrode material in the process of continuous constant voltage charge and discharge. It proved that the introduction of cerium has promoted electron transfer, which improved the electrochemical performance of electrode material. In this paper, compared with WO3-CNFs without Ce, the Ce/WO3-CNFs have wide lattice spacing and hydrophilicity, fully contact with the electrolyte in the electrochemical reaction, and provide high electron transfer ability. The Ce/WO3-CNFs shows the maximum specific capacitance (407 F g−1) and excellent cycling stability (10,000 cycles at 5 A g−1 with a retention rate of 80 %). Otherwise, the flexible asymmetric supercapacitor device was prepared using the Ce/WO3-CNFs as cathode, and the CNFs as the anode, which exhibited the maximum energy density was 35.75 Wh kg−1 and a power density was 362.54 W kg−1 at 0.5A g−1. The results show that rare earth doping is an effective way and that the Ce/WO3-CNFs are promising electrode materials for supercapacitors.

Constructing superior rate-performance manganese-based anode for lithium-ion batteries by tuning interface effect

Interface engineering is an effective way to improve the electrochemical performance of electrode materials for LIBs. Point contact interfaces in composites are constructed by growing of Mn3O4 nanoparticles on the surface of acetylene black (AB). The prepared electrode materials exhibit excellent rate capability (355.7 mAh g−1 at 6.4 A g−1) and cycling stability (1386.7 mAh g−1 after 300 cycles at 1 A g−1). The presence of AB in the composite reduces the charge transfer resistance and improves the cycling stability of the electrode. Moreover, the interface between the composites increases the contribution of pseudocapacitance, which will facilitate the electrode kinetics. The construction of interfaces in the composites provides a promising perspective for the design of high-power density anode for LIBs. Highlights Construction of Mn3O4 nanoparticles on 0 D-AB spheres was proposed and synthesised by a facile and scalable strategy. The composite materials exhibit excellent electrochemical performance. The superior rate performance is mainly attributed to the interface effect of composite material.

Constructed multifunctional CuOx core and electrodeposited nickel‑cobalt sulfide for high areal energy-power density supercapacitor

Construction of heterostructure is regarded as an effective strategy for enhancing the electrochemical performance of electrode materials for supercapacitor. Moreover, the relatively poor conductivity and commonly structural design severely decrease the electron transfer ability and surface utilization of nickel cobalt sulfides during charge-discharge process. In this work, three unique core structures of Cu, CuO, and CuOx (Cu-Cu2O-CuO) were successfully constructed on copper foam via an in-situ redox strategy. Among them, the CuOx cores exhibit higher capacity and lower voltage drop because of the high conductivity of Cu, the generation of built-in electric field between Cu2O and CuO, as well as rich active areas. Three-dimensional interconnected NiCoS nanosheets grown on the surface of CuOx cores with high areal-loading and robust interfacial adhesion. Benefited from the unique structural advantages and synergistic effect of multi-metallic active centers, the CuOx/NiCoS composite exhibits high specific capacitance of 3305 mF cm−2 at 5 mA cm−2, outstanding rate capability of 68.3% when the current density increases to 60 mA cm−2, and long-term lifespan. Notably, the assembled CuOx/NiCoS//PAC asymmetric supercapacitor delivers a high areal energy density and power density (263.3 μWh cm−2 at 2.4 mW cm−2), which can drive some small electronic devices. This study offers a novel pathway for further design of a core-shell structured electrode materials with an enhanced capacity and rate capability for advanced energy storage devices.

Activation-Assisted High-Concentration Phosphorus-Doping to Enhance the Electrochemical Performance of Cobalt Carbonate Hydroxide Hydrate.

P-doping into metal oxides has been demonstrated as a valid avenue to ameliorate electrochemical performance because it can tune the electronic structures and increase the active sites for an electrochemical reaction. However, it usually results in a low P-doping concentration via the commonly used gas phosphorization method. In this work, an activation-assisted P-doping strategy was explored to significantly raise the P-doping concentration in cobalt carbonate hydroxide hydrate (CCHH). The activation treatment increased active sites for electrochemical reaction and endowed the sample with a high P content in the subsequent gas phosphorization process, thereby greatly enhancing the conductivity of the sample. Therefore, the final CCHH-A-P electrode exhibited a high capacitance of 6.62 F cm-2 at 5 mA cm-2 and good cyclic stability. In addition, the CCHH-A-P//CC ASC with CCHH-A-P as the positive electrode and carbon cloth as the negative electrode provided a high energy density of 0.25 mWh cm-2 at 4 mW cm-2 as well as excellent cycling performance with capacitance retention of 91.2% after 20,000 cycles. Our work shows an effective strategy to acquire Co-based materials with high-concentration P-doping that holds great potential in boosting the electrochemical performance of electrode materials via P-doping technology.

Facile Synthesis of Sea-Urchin-like VN as High-Performance Anode for Lithium-Ion Batteries

Lithium-ion batteries are still the main theme of the contemporary market. Commercial graphite has struggled to meet the demand of high energy density for various electronic products due to its low theoretical capacity. Therefore, exploring for a new anode with high capacity is important. Vanadium nitride has attracted widespread attention due to its high theoretical specific capacity and good chemical/thermal stability. However, vanadium nitride is accompanied by huge volume expansion and nanoparticle agglomeration during the electrochemical reaction, which limits its application. Herein, sea-urchin-like vanadium nitride (SUK-VN) was successfully prepared with a simple hydrothermal method combined with an annealing strategy to boost the actual capacity of the vanadium nitride. The special sea-urchin-like morphology effectively suppresses the agglomeration of vanadium nitride nanoparticles and exposes more reactive sites, which facilitates the electrochemical performance of electrode materials. In the half-cells, sea-urchin-like vanadium nitride exhibits a specific capacity of 361.5 mAh g−1 at 0.1 A g−1 after 60 cycles, and even still achieves a specific capacity of 164.5 with a Coulomb efficiency of approximately 99.9% at 1 A g−1 after 500 cycles. Such a strategy provides the potential to enhance the electrochemical properties of vanadium nitride anodes in terms of solving the nanoparticle agglomeration.

Effect of microstructure on electrochemical performance of electrode materials for microsupercapacitor

Recently, many popular methods, such as vacuum filtration, spray coating and electrophoretic deposition, have been employed for assembling Ti3C2Tx MXene based micro-supercapacitors (MSCs). However, different preparation techniques affect the microstructure of electrode, and further affect the electrochemical performance, which has been rarely reported. Then the electrochemical performance of electrodes via above preparation technologies has been studied. By contrast, the electrode prepared by electrophoretic deposition possesses more open structure. The optimized device delivers high areal capacitance, good rate capability and excellent flexibility.

A positive electrode with thoughtful diffusion capacitance for solid flexible supercapacitor: N-6 doped porous carbon shell coated Cu doped Mn[sbnd]Co LDO core

The suitable proportion of diffusion contribution during the electrochemical process could influence the electrochemical performance of electrode materials. An effective method is that tuning the diffusion reaction contribution via doping heteroatom, introducing defects or surface modification. In this work, a unique core-shell structure material Cu-Mn-Co LDO-C is obtained. Benefitting from Cu pre-doped into MnCo LDO, large amount of oxygen vacancies is introduced to enhance electrochemical performance; N-6 doped porous carbon shell protects Cu-Mn-Co LDO core and improves electrochemical performance of Cu-Mn-Co LDO-C further. In addition, doping Cu broadens potential window of Cu-Mn-Co LDO-C surprisingly. Cu-Mn-Co LDO-C presents 5028.7 mF cm−2 at a current density of 1 mA cm−2 with a facilely reached potential window of 0–0.65 V finally, and retains 73.4 % diffusion contribution at a scan rate of 1 mV s−1, 18.3 % at 100 mV s−1. After 10,000 cycles at 2 mA cm−2, Cu-Mn-Co LDO-C keeps 90.3 % of initial capacitance. Using Cu-Mn-Co LDO-C as positive and Fe3O4-C as negative to fabricate a solid flexible asymmetrical supercapacitor (SAS), this SAS presents a considerable energy density that attribute to the high working potential of positive Cu-Mn-Co LDO-C. SAS could working stably at a potential window of 0–2.2 V, and presents the highest energy density 243.1 μWh cm−2 at a power density of 2.8 mW cm−2, remains 203.0 μWh cm−2 at the highest power density of 55.4 mW cm−2. A hand ring that was assembled by three SAS which contacted in series could light a highest rated voltage white LED more than 10 min. As a result, Cu-Mn-Co LDO-C is an ideal candidate for flexible positive electrode in the field of smart, portable energy storage.

Atomic surface regulated nanoarchitectured MnCo2S4@ALD-CoOx positrode with rich redox active sites for high-performance supercapacitors

Multi-metal sulfide nanoarchitecture materials can enhance the performance of supercapacitors by increasing the redox active sites and surface reaction kinetics via the facilitation of more ions/electron pathways. The surface morphologies and developing technology of nanoarchitecture materials significantly affect the electrochemical performance of electrode materials. Therefore, this study deposits an atomic layer of CoOx on MnCo2S4 nanoneedles to develop a potential positrode that can deliver outstanding electrochemical behavior and cycle performance characteristics. The MnCo2S4 nanoneedles are fabricated using a two-step hydrothermal–sulfidation method. Results reveal that the atomic layering of 10-nm CoOx on the surface of MnCo2S4 nanoneedles enhances the specific capacity (to 628C/g (1396F/g)) at a current density of 3 A/g compared to those of pristine MnCo2S4 and other atomic layer-deposited materials owing to the low charge transfer resistance and high surface active sites of the optimized material. Furthermore, an asymmetric supercapacitor device is fabricated using the 10-nm CoOx atomic-layered MnCo2S4 as the positrode, and activated carbon as the negatrode. The fabricated device delivers a maximum energy density of 78.67 Wh/kg at a power density of 847 W/kg and stable 8000 charge–discharge cycles at a current density of 5 A/g. The improvement in the electrochemical performance can be attributed to the combined contribution of both components (i.e., atomically-layered CoOx and unique core–shell nanoarchitecture).

Overlooked impact of precursor mixing: Implications in the electrochemical performance of battery electrode materials

Solid-state reactions are an essential part of the synthesis of various cathode materials for lithium-ion batteries (LIBs). Despite the simplicity and effectiveness for mass production, a subtle variation in synthesis conditions can often give rise to unexpectedly different physical properties, significantly affecting the electrochemical performance of electrode materials. However, this aspect has long been overlooked in the LIB community, which should focus on advancement in understanding the influence of synthesis conditions. As solid-state reactions occur only at the interface of precursor materials, maximizing the interfacial contact area between mixed precursor powders is crucial. Mechanical milling and/or mixing are common practices that have been performed in both academia and industry for this purpose. Unlike the common belief that this pre-treatment before calcination would be of great benefit for the preparation of high-performance LIB materials, we revealed in this work that this practice is not always successful for this goal. In our case study of the preparation of LiCoO2, we demonstrated that mechanical mixing—a routinely implemented process for homogeneous mixing of precursors—can be harmful if it is performed without assuring optimal working conditions for mixing. The underlying reasons for this surprising result are elucidated in this work, and we hope that this new insight can help avoid the potential pitfall of routine implementations performed for LIB materials.

Mass and Charge Transfer in a Polymeric NiSalen Complex at Subzero Temperatures

Electrochemical energy storage systems have a wide range of commercial applications. They keep energy and power even at temperatures up to +60 °C. However, the capacity and power of such energy storage systems reduce sharply at negative temperatures due to the difficulty of counterion injection into the electrode material. The application of organic electrode materials based on salen-type polymers is a prospective approach to the development of materials for low-temperature energy sources. Poly[Ni(CH3Salen)]-based electrode materials synthesized from different electrolytes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and quartz crystal microgravimetry at temperatures from -40 °C to 20 °C. By analyzing data obtained in various electrolyte solutions, it was shown that at subzero temperatures, the process of injection into the polymer film, together with slow diffusion within the film, predominantly limit the electrochemical performance of electrode materials based on poly[Ni(CH3Salen)]. It was shown that the deposition of the polymer from solutions with larger cations allow the enhancement of the charge transfer due to the formation of porous structures facilitating the counter-ion diffusion.

Enhancing supercapacitor performance using nanosheet-covered nanotube structures Co3S4/Ni0.96S@CNTs with carbon nanotubes as conductive substrates.

Transition metal sulfides have broad application prospects as supercapacitor electrode materials. However, their poor structural stability and conductivity hinder improvements in their electrochemical performance. Therefore, the introduction of highly conductive carbon nanotubes (CNTs) as sulfide growth substrates is considered to improve the microstructure and electrochemical performance of electrode materials. In this study, a highly conductive CNT solution was sprayed onto a nickel foam current collector, and Co3S4/Ni0.96S was successfully constructed on a CNT conductive substrate using a combination of hydrothermal and electrochemical deposition methods, forming a unique nanosheet-covered nanotube structure Co3S4/Ni0.96S@CNTs. The addition of an appropriate concentration of CNTs can not only serve as a substrate for the growth of Co3S4/Ni0.96S, but also effectively maintain the overall nanosheet structure. Thus, the Co3S4/Ni0.96S@CNTs (2-CSNS@CNTs) have a stable structure and a wide range of electrochemical reaction sites, ensuring excellent conductivity and cycling stability. The electrode material 2-CSNS@CNTs exhibited a specific capacity of 1427.05 C g-1 at 1 A g-1. Additionally, the asymmetric supercapacitor 2-CSNS@CNTs exhibited a high energy density of 53.76 W h kg-1 at 800 W kg-1 and a capacity retention rate of 68.5% at 10 A g-1 after 1000 cycles.

Hydrothermal synthesis of nano-sized MnO2 supported on attapulgite electrode materials for supercapacitors

Among the electrode materials of supercapacitors, transition metal oxides have been widely used because of their low price, high theoretical capacitance and good cycle stability, and MnO2 is one of the typical representative materials. However, the actual specific capacitance of MnO2 is low because of its poor conductivity, easy agglomeration in the preparation process and large volume change in the process of repeated charge and discharge. Attapulgite can not only provide a large specific surface area for transition metal oxide materials, but also provide a skeleton on which nano-sized materials can be grown or dispersed. Therefore, the electrochemical performance of electrode materials can be improved by designing nanostructures and compounding a variety of materials with different properties. Herein, a new type of composites electrode material is prepared by simple one-step hydrothermal method. As an electrode material, the ATP-MnO2 composites exhibited a high specific capacitance of 138.2 F/g at a current density of 0.5 A/g, which was 13.4% higher than that of pure MnO2 nanoflowers. Under the current density of 3 A/g, the capacitance retention of ATP-MnO2 composites was 89.4% after 5000 cycles.

Atomic-level understanding on progressive lithiation of few-layer MoS2 with surface vacancies

Vacancy engineering is a powerful modification strategy to elevate the electrochemical performance of electrode materials. In this work, the impacts of various surface vacancies in few-layer molybdenum disulfide (MoS2) on Li adsorption/intercalation and diffusion at both MoS2 surface and interlayers are systematically investigated to advance the material performance using first-principles calculations. The results show that the surface vacancy in few-layer MoS2 is easier to form than internal ones, and surface single S vacancy (VS) is the most stable. All seven surface vacancies can promote Li adsorption and intercalation at MoS2 surface and interlayer, and have a much more beneficial role on Li surface adsorption than interlayer intercalation. Surface single Mo vacancy (VMo) can upgrade the diffusion rate of Li at the few-layer MoS2 surface and nearby interlayer, and VS has a neglected impact on the rate capability. VMo is found to be the most propitious vacancy type for Li binding and diffusion at the few-layer MoS2. This theoretical exploration can help the comprehension of the impact of vacancies on the Li adsorption, intercalation, and transportation at the surface and interlayers of the dichalcogenides as high-performance electrode materials for rechargeable batteries.

Contribution of calcium ion doping to the rate property for LiFe0.5Mn0.5PO4/C

Exotic atom doping is one of the crucial measures to improve the electrochemical performance of electrode materials. The calcium-doped LiFe0.5Mn0.5PO4@C (LFMP/C-Ca) was effectively fabricated by high temperature solid-state reaction. The XRD Rietveld refinement results show that calcium ion doping increases the lattice parameters of the LFMP/C. Compared to LFMP/C, the LFMP/C-3Ca provides superior cycling stability and rate property. The galvanostatic intermittent titration (GITT) results show that LFMP/C-3Ca possesses a larger lithium-ion diffusion coefficient than LFMP/C. The experimental results show that LFMP/C-3Ca possesses a superior electronic conductivity, which is also proved by density function theory (DFT) calculations. At high rates, the discharge specific capacities of LFMP/C-3Ca are 105.7 mAh g−1, 94.7 mAh g−1, 84.9 mAh g−1, 70.8 mAh g−1 and 53.1 mAh g−1 at 10C, 20C, 30C, 40C, 50C, respectively. Therefore, the appropriate calcium doping is helpful to improve rate performance of LiFe0.5Mn0.5PO4@C.

Lithium Vanadium Oxide/Graphene Composite as a Promising Anode for Lithium-Ion Batteries

Lithium vanadium oxide (Li3VO4, LVO) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity (394 mAh g-1) and safe working potential (0.5-1.0 V vs. Li+/Li). However, its electrical conductivity is low which leads to poor electrochemical performance. Graphene (GN) shows excellent electrical conductivity and high specific surface area, holding great promise in improving the electrochemical performance of electrode materials for LIBs. In this paper, LVO was prepared by different methods. SEM results showed the obtained LVO by sol-gel method possesses uniform nanoparticle morphology. Next, LVO/GN composite was synthesized by sol-gel method. The flexible GN could improve the distribution of LVO, forming a high conductive network. Thus, the LVO/GN composite showed outstanding cycling performance and rate performance. The LVO/GN composite can provide a high initial capacity of 350.2 mAh g-1 at 0.5 C. After 200 cycles, the capacity of LVO/GN composite remains 86.8%. When the current density increased from 0.2 C to 2 C, the capacity of LVO/GN composite only reduced from 360.4 mAh g-1 to 250.4 mAh g-1, demonstrating an excellent performance rate.

Understanding the Predominant Potassium-Ion Intercalation Mechanism of Single-Phased Bimetal Oxides by in Situ Magnetometry

The electrochemical performance of electrode materials is largely dependent on the structural and chemical evolutions during the charge-discharge processes. Hence, revealing ion storage chemistry could enlighten mechanistic understanding and offer guidance for rational design for energy storage materials. Here, we investigate the mechanisms of potassium (K)-ion storage in the promising bimetal oxide materials by in situ magnetometry. We focus on a single-phased hollow FeTiO3 (SPH-FTO) hexagonal prism synthesized through a complexing-reagent assisted approach and find that the K-ion storage in this compound occurs predominantly with an intercalation mechanism and fractionally a conversion mechanism. We also demonstrate a K-ion hybrid capacitor assembled with the prepared SPH-FTO hexagonal prism anode and activated carbon cathode, delivering a high energy density and high power density as well as extraordinary cycling stability. This new understanding is used to showcase the inherently high K-ion storage properties from the earth-abundant FeTiO3.