Ternary Cathode Blend Electrodes for Environmentally Friendly Lithium-Ion Batteries.

The demand for battery cells with increased energy density without sacrificing performance is driving research into investigating new active electrode materials. The addition of silicon oxide as a second active anode material alongside graphite, referred to as graphite/SiOx blend electrodes, offers a great opportunity to increase the specific capacity of lithium-ion cells. The stable structure of graphite in combination with the high theoretical capacity of silicon represents a promising improvement, for example to increase the driving range of electric vehicles.In this work, the electrochemical behavior during the lithiation and delithiation process of blend electrodes is analyzed. Two custom-made cells are connected in parallel, with each of the cells containing either pure graphite or pure SiOx as the working electrode. Both cells use similar counter electrodes. The experimental setup enables the measurement of the current distribution during charging or discharging of the parallel connection. The observed individual current flow to each cell represents the current flow to each active material. This allows conclusions to be drawn about of the electrochemical processes in a graphite/SiOx blend electrode [1].This work focuses on two effects of blend electrodes: First, the lithiation differences between the active materials with increasing charge rates. Changes in the lithiation distribution between the active materials are observed at higher currents. Second, the effect of hysteresis on the lithiation of blend electrodes. When stating the lithiation process with a fully or partially delithiated blend electrode, the increased delithiation potential of SiOx [2] causes differences in the lithiation distribution between the materials. The knowledge gained on graphite/SiOx blend electrodes contributes to a better understanding of lithium-ion cells and to the optimization of their integration in electric vehicles.

Lithium-ion battery (LIB) technology is the key enabler of energy storage and electric propulsion. Today´s LIB technology was primarily developed for applications in consumer electronics and is now transferred into automotive applications. These applications demand high specific capacity in order to provide a long driving range as well as high power densities for acceleration, recharging and recuperation. So far, state-of-the-art Lithium-ion batteries do not fully meet the requirements of automotive applications with respect to energy density, power density, extended life time, cost and safety. The commercialized LiFePO4 exhibits good rate capability. Energy density is below that of commercially used layered oxides due to its redox plateau at 3.5 V. A lot of interest is therefore drawn to the isostructural LiMnPO4 due to its higher redox plateau of 4.1 V vs. Li/Li+, which is able to provide higher energy densities [1,2]. Unfortunately, pure LiMnPO4 suffers from low rate capability. On material level, Yamada et al. demonstrated that the partial substitution of manganese in LiMnPO4 with iron, Li(MnxFe1-x)PO4 (LFMP) leads to an improved electrochemical performance and increased energy density [3,4]. On electrode level, a promising strategy to further adjust the electrochemical behavior is to custom-tailor properties by blending complementary types of cathode materials [5-7]. In order to enhance the limited kinetics of manganese based olivine, blending with LiMn2O4-Spinel is expected to result in a promising cathode material for two reasons: a) spinel show fast kinetics, as can be observed from a less pronounced voltage decay at higher C-rates and b) provide a redox plateau in a range comparable to LFMP. Blend electrodes are prepared by mixing the olivine LiFe0.3Mn0.7PO4 (LFMP) and LiMn1.9Al0.1O4 spinel (LMO) in order to obtain a composite electrode, combining the high capacity of LFMP and the rate capability of the spinel. Electrode characteristics are compared with theoretical calculations based on experimental data obtained from electrodes of the single components LFMP and LMO. While tap density of the powders and electrode parameters show a linear dependency on the blend ratio, remarkable synergetic effects can be observed regarding the electrochemical performance at high rates (3C). Potential curves of blend electrodes at rates of 3C reveal a less pronounced voltage decay for the Mn2+/3+plateau than expected from theoretical calculations as depicted in Figure 1a. This buffer effect is also observed for high current pulses (5C) where blend electrodes resemble the behavior of pure spinel electrodes. In terms of power density at high states of charge (SoC), the performance of the investigated blends exceeds even that of pure spinel. In addition, the spinel-related manganese dissolution can be drastically reduced by blending spinel with LFMP. Structural changes in blend electrodes during pulse power discharge of the manganese redox plateau are investigated with in-situ XRD measurements. Shifts in XRD pattern during relaxation (I = 0) gives us indication of particle-to-particle interactions between LFMP and LMO. Figure 1b illustrates a comparison between the battery relevant features of LFMP, spinel and a blend with LFMP:LMO = 50:50 cap%. This study shows the expected and synergetic effects of LFMP/spinel blends and compares the results with theoretical calculations [8]. The complementary properties of the single component materials LFMP and spinel result in a cathode material which can be promising for 48V starter batteries in automotive applications, where high power densities at high states of charge are required in order to start the internal combustion engine.

The use of electrodes with multiple active materials is considered a promising approach to develop advanced Li‐ion batteries. Recent studies even point to synergistic effects in terms of rate performance. However, the origin of synergistic effects is still insufficiently understood to enable targeted material and design development and to optimize batteries accordingly. Using straightforward equivalent circuit modeling combined with electrochemical studies, we reveal that improvements in rate capability are an intrinsic property of blended electrodes. The electrical parallel connection of the components in the composite electrode allows the applied current to be distributed among the components in a way that the voltage losses become minimal. This way, rate‐limiting components can still contribute to the electrode's capacity at high loads, which makes blended electrodes particularly attractive, e. g., for applications that must be able to handle high pulse loads. Based on the results, rational design principle are derived by means of a systematic sensitivity analysis, quantifying the influence of the individual active material properties. These findings greatly contribute to the understanding of the internal dynamics and synergy effects in blended electrodes and support the targeted development of advantageous material combinations and electrode designs for future Li‐ion batteries.

1. Purpose Solid-state lithium-ion batteries (SSLIBs) have attracted extensive attentions because of their potentials to improve safety and to achieve higher power and energy densities compared with the conventional lithium-ion batteries. In composite electrodes for SSLIBs, particles of active material (AM) and solid electrolyte (SE) are three-dimensionally distributed and form complicated Li-ion and electron pathways. Then, especially during high rate charging/discharging, the inhomogeneous reaction distribution may be formed in the electrode. The reaction distribution can substantially deteriorate the battery performances of SSLIBs such as capacity, power output, rate capability, and cyclability. Therefore, understanding how the reaction distribution affects the battery performances is crucial for the development of high-performance SSLIBs. In this study, we performed operando three-dimensional (3D) observation of reaction distributions in composite electrodes for SSLIBs using CT-XAFS1 to elucidate the influence of reaction distributions on the battery performances of SSLIBs. 2. Experimental An SSLIB cell with a configuration of Li x CoO2 (LCO)-Li2.2C0.8B0.2O3 (LCBO) composite electrode|LCBO electrolyte|poly (ethylene oxide) (PEO)-based polymer electrolyte|Li metal electrode was fabricated based on the literature2. The composite electrode comprised 8 mg of LCO and 2 mg of LCBO. The SSLIB cell was charged to 4.5V and discharged to 2.0 V with a current of 240 μA (0.3 C) for 3 cycles at 100 °C. The reaction distribution in the composite electrode was observed every 40 minutes during charging and discharging using operando CT-XAFS. The CT-XAFS measurements were carried out in the energy range between 7725.5-7730 eV with an energy step of 0.1 eV under an exposure time of 20 ms per energy and projection angle from -65 to 65° with an angle step of 0.1°. The observation area was 517 × 517 × 49 μm. The spatial and time resolutions were 3.1 μm and 40 min., respectively. 3. Results and Discussion Figure 1(a) shows the charge-discharge curves of the SSLIB cell. The SSLIB cell exhibited the initial charge and discharge capacities of 84 and 46 mAh·g−1, respectively. Those degraded to 24 and 13 mAh·g−1 in the 2nd cycle, and 12 and 12 mAh·g−1 in the 3rd cycle, respectively. Figure 1(b) shows the 3D charging state (Li content) maps of the composite electrode and the representative 2D cross-sectional charging state maps in the in-plane direction at the end of 1st, 2nd, and 3rd charge. Colored/uncolored areas stand for the regions where the AMs exist or not, respectively. The red/blue areas stand for the charged (x = 0.6) /discharged (x = 1.0) AMs, respectively. After the 1st charge, the AMs generally showed a high charging state (red). However, the regions with high charging state significantly decreased after the 2nd charge, and most of the AMs showed a charging state corresponding to x = 0.7 ~ 0.8 (green). The regions with high charging state further decreased after the 3rd charge, and AMs with a low charging state were increased (blue). To more precisely investigate where the less-charged AMs existed after the 2nd and 3rd charge, we subtracted the charging state map after the 1st discharge from that after the 2nd charge, and also the charging state map after the 2nd discharge from that after the 3rd charge (Fig. 1(c)). The 2D maps in Fig. 1(c) thus indicate to what extent the charge reaction progressed during the 2nd or 3rd charge compared with the end of the 1st or 2nd discharge, respectively. The red/blue areas in Fig. 1(c) represent the AM regions where the reaction progressed (Δx = 0.4) or not (Δx = 0) from the end of the 1st or 2nd discharge, respectively. As shown in the left map in Fig. 1(c), the inner parts of the aggregated AMs were significantly less charged compared to the regions near AM/SE interfaces during the 2nd charge. Similarly to the 2nd charge, the charge reaction preferentially progressed near the AM/SE interfaces, while the reaction insufficiently progressed at the inner parts of the aggregated AMs during the 3rd charge. Such a variation in the charging state distribution during cycling could be explained by considering the microstructural change due to the expansion/shrinkage of AM particles. The above results suggest that the expansion/shrinkage of AM particles reduced the connections between AM particles but did not reduce the AM/SE interfaces. We further discuss the mechanism of the capacity degradation during cycling in the presentation.

Increasing concerns about environmental and energy problems accelerate the demands for high-energy-density batteries. Lithium-ion batteries (LIB) have large energy densities and have been well applied on not only portable devices such as smart phones but also electronic vehicles (EV). However, the energy densities of present LIBs for EV-use seem not to satisfy for a long cruising distance. Present LIBs for EV-use possess large power densities by the sacrifice of energy densities in order to shorten the charging time. In the practical LIBs for portable devices, dense and thick composite electrodes are used. In this case, the ion transport of electrolyte solution through the pores in the composite electrodes becomes a slow process. In order to enhance the energy densities with remaining high power densities, the ion transport rate should be increased for the dense and thick composite electrodes. Unfortunately, to develop dense and thick electrodes with high power densities, fundamental understanding of the ion transport in composite electrodes has not been clear. In this study, ion transportation behavior was investigated with ac impedance spectroscopy. In a conventional use of ac impedance spectroscopy, a composite electrode is used as a working electrode of the measurement cell. In this case, the result of impedance spectroscopy contains all resistances and capacitances accompanying the whole of the charge and discharge reaction including ion transfer through electrolyte and active materials, ion diffusion within active materials, etc. To focus on the impedance of ion transportation of electrolyte, it must be discriminated from that derived from other reaction steps. In order to obtain impedance spectra derived from only ion transportation, composite electrodes without a current collector were used. As a result, we obtained semi-circles, and this semi-circle was assigned to the ion transport process through the graphite composite electrode. As the potential went down, two semi-circles were observed. The characteristic frequency and the resistance of the semi-circle at higher frequency almost did not change. However, at lower frequency, the characteristic frequency and resistance changed. Further, we used a model electrode to understand the semi-circles. The detail analysis will be presented at the meeting.

ConspectusLithium-ion batteries (LIBs) are nearly ubiquitous energy storage solutions, powering devices ranging from consumer electronics to electric vehicles. To advance these applications, current LIB research efforts are directed toward improving energy and power densities, cyclic lifetimes, charging speeds, and safety. These parameters are intrinsically tied to properties of the active electrode materials, such as the redox mechanism, chemical composition, and crystal structure. One particularly challenging issue is that the active electrode materials that possess higher theoretical energy densities are generally more susceptible to degradation during cycling. A notable example is the family of layered multicomponent transition metal oxides, which is the incumbent class of active LIB cathode materials for electric vehicles. To increase their theoretical capacities, the transition metal fraction in these materials is trending toward higher Ni content. However, Ni-rich chemistries suffer from electrochemical, crystallographic, and mechanical degradation that increase in severity with increasing Ni content. Furthermore, alternative high-energy cathode materials, including overlithiated layered oxides and disordered rock salt materials, present additional stability challenges that must be overcome before they can be realistically incorporated into LIB technology.The chemomechanical degradation in high-energy LIB cathode materials occurs at multiple length scales. Point defects, such as antisite defects or vacancies, are commonly generated during electrochemical cycling and can contribute to the loss of cyclable active material. At both the primary and secondary particle level, electrochemical cycling also induces significant volumetric changes and state-of-charge heterogeneity, generating regions of high stress and strain that are precursors to mechanical fracture. Finally, at the electrode level, nonuniform charge transfer reactions throughout the electrode can lead to locally overcharged regions that become sites of enhanced degradation. To address these issues, active cathode material design and electrode engineering are being heavily pursued to accelerate improvements in LIB energy density. To consolidate the current understanding of chemomechanical degradation and provide guidance on mitigation strategies, a comprehensive overview of degradation mechanisms across multiple length scales is critically needed.In this Account, we first outline the origins of chemomechanical degradation for high-energy LIB cathodes, including layered oxides, overlithiated layered oxides, and disordered rock salt structures. Specifically, we delineate the thermodynamic and kinetic origins of defect generation at the atomic level and then progress to the kinetic origins of broader degradation mechanisms at the particle level and electrode level. Next, we discuss strategies for minimizing chemomechanical degradation in high-energy LIB cathodes at multiple length scales. Finally, we provide a forward-looking perspective on how to accelerate progress toward practical high-energy LIB cathodes, including emerging methods to map state-of-charge heterogeneity, efficient data processing techniques, and improved strategies for spatially identifying chemomechanical degradation. We also propose engineering solutions for mitigating chemomechanical degradation, such as grain boundary engineering, modifying the active material particle morphology, and electrode architecture design. Since many of these suggestions can be applied irrespective of cathode chemistry, this Account is likely to be broadly applicable to the diverse set of ongoing efforts to realize high-energy LIBs.

Strategies for formulation optimization of composite positive electrodes for lithium ion batteries based on layered oxide, spinel, and olivine-type active materials

We develop zirconium-templated NiO/NiOOH nanosheets on nickel foam and polypyrrole-embedded in exfoliated carbon fiber cloth as complementary electrodes for an asymmetric battery-type supercapacitor device. We achieve high volumetric energy and power density by the modification of commercially available current collectors (CCs). The modified CCs provide the source of active material, actively participate in the charge storage process, provide a larger surface area for active material loading, need no additional binders or conductive additives, and retain the ability to act as the CC. Nickel foam (NF) CCs are modified by use of a soft-templating/solvothermal treatment to generate NiO/NiOOH nanosheets, where the NF is the source of Ni for the synthesis. Carbon-fiber cloth (CFC) CCs are modified by an electrochemical oxidation/reduction process to generate exfoliated core-shell structures (ECFC). Electropolymerization of pyrrole into the shell structure produces polypyrrole embedded in exfoliated core-shell material (PPy@rECFC). Battery-type supercapacitor devices are produced with NiO/NiOOH@NF and PPy@rECFC as positive and negative electrodes, respectively, to demonstrate the utility of this approach. Volumetric energy densities for the full-cell device are in the range of 2.60-4.12 mWh cm-3 with corresponding power densities in the range of 9.17-425.58 mW cm-3. This is comparable to thin-film lithium-ion batteries (0.3-10 mWh cm-3) and better than some commercial supercapacitors (<1 mWh cm-3).1 The energy and power density is impressive considering that it was calculated using the entire cell volume (active materials, separator, and both CCs). The full-cell device is highly stable, retaining 96% and 88% of capacity after 2000 and 5000 cycles, respectively. These results demonstrate the utility of directly modifying the CCs and suggest a new method to produce high volumetric energy density and power density storage devices.

AgNP is synthesized on the surface of F-graphene as anchored, and characterized to form less than 20 nm in size having quantized physical properties. Application of AgNP has been investigated its effects on NiO/Ni(OH)2 supercapacitor from the comparison of specific capacitance (F g-1) and capacity (mA h g-1). It shows to be beneficial to the energy and power density of NiONi(OH)2 with reversible AgNP multi redox reactions. The specific capacitance of NiONi(OH)2 is highly enhanced by applied AgNP anchored on F-graphene (AgNP/F-graphene) from 148 F g-1 to 356 F g-1 while it results in 226 F g-1 by applied silver without F-graphene. The best result is obtained with the nafion free electrode of AgNP/F-graphene/NiONi(OH)2, as it results in 1,153 F g-1 at the experimental condition of 5 mV/s scan rate in 1M KOH. For the specific capacity of NiO/Ni(OH)2, the identical result is observed as it improved from 266 mA h g-1 up to 545 mA h g-1 by applied AgNP anchored on F-graphene. The performance of AgNP combined NiONi(OH)2 leads us to explore the secondary battery of Zn-Ni that combined with Zn-Ag. A preliminary galvanic-charge/discharge test using a single cell of AgNP/F-graphene/NiONi(OH)2 coupled with Zn plate demonstrates to be a potential hybrid rechargeable battery having a high power and energy density, as it resulted in about 3,433 W kg-1 for the power density and 958 W h kg-1 for the energy density, respectively, on the basis of Ni and Silver as the active material.

An approach to improve the performance of positive electrodes for Li-ion batteries that is commonly used by companies is fabricating them using mixtures of different materials (usually 2) with complementary features1. This coexistence, when properly formulated, provides an extra design degree of freedom and gives rise to synergetic effects, allowing blends to perform better than what the rule of mixture predicts. Unfortunately, the internal dynamics of the electrodes are still poorly understood at fundamental level and the optimization of formulations for such blends still mainly depends on empirical studies. One of the important characteristics identified in blends is termed the buffer effect. This occurs when the material exhibiting fastest kinetics can receive an excess of the incoming lithium under high power discharge and subsequently, when the current stops, transfer this excess to the higher capacity material.In this study, the role and extent of this effect is explored for a set of representative materials and the resulting blends resulting from their mixtures. For the measurements we are using a special experimental model-like blended electrode setup reported by Heubner et al.2 slightly adapted to our needs. In this setup, two positive electrodes with different active material, but same active mass, are facing each other, separated by 2 separators with a disk of perforated lithium in the middle. During measurement, current is applied between an electrode and lithium while a potentiostat actively keeps the two positive electrodes at the same potential. Such setup gives us access to the current exchanged between the positive electrodes while keeping them in equal potential at all times, as would happen in a blended electrode with 50% of each material.For the study, 4 cathode active materials were used, LiNi0.5Mn0.3Co0.2O2 (NMC), LiMn2O4 (LMO), LiFePO4 (LFP) and LiFe0.4Mn0.6PO4 (LFMP), and every binary combination of them was measured. The cells after 3 C/10 formation cycles were subjected to a pulsed electrochemical test (1 minute 3C pulses followed by 10 minutes of relaxation). Top figure shows the voltage response of the cell vs. time while the bottom one shows the charge that was transferred between the materials during their relaxations (buffering charge) and while the cell current is equal to zero , for the NMC-LMO blend. We applied the same protocol for all the combinations under study and found out large variations of this buffering ability depending on the blends constituents and their individual electrochemical properties. It is clearly evident that both the magnitude and the direction (sign) of the buffering current varies in the voltage range meaning each material can act as donor or acceptor of the buffering lithium. We believe that this provides a new insight in the internal processes in blended electrodes and brings us one step closer to their rational design. References : Casas‐Cabanas et al. Isr J Chem 61, 26–37 (2021).Heubner et al. J Power Sources 363, 311–316 (2017). Figure 1

Strontium phosphide-polyaniline composites for high performance supercapattery devices

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

This review discusses the contribution of physical vapor deposition (PVD) processes to the development of electrochemical energy storage systems with emphasis on solid‐state batteries. A brief overview of different PVD technologies and details highlighting the utility of PVD for the fabrication and characterization of individual battery materials are provided. In this context, the key methods that have been developed for the fabrication of solid electrolytes and active electrode materials with well‐defined properties are described, and demonstrations of how these techniques facilitate the in‐depth understanding of fundamental material properties and interfacial phenomena as well as the development of new materials are provided. Beyond the discussion of single components and interfaces, the progress on the device scale is also presented. State‐of‐the‐art solid‐state batteries, both academic and commercial types, are assessed in view of energy and power density as well as long‐term stability. Finally, recent efforts to improve the power and energy density through the development of 3D‐structured cells and the investigation of bulk cells are discussed.

The performance of Ni-foam pasted Ni(OH)2 prepared from co-precipitated Ni(OH)2 with Zinc (Zn) and Cobalt (Co) as the positive electrode active material of an asymmetric electrochemical capacitor (EC) is studied for the enhancement of the capacitor’s specific energy and power densities. A co-precipitated Ni(OH)2/activated carbon (AC) composite material and AC were used as a positive and negative electrode material. The AC in the positive electrode is used as an electrolyte reservoir to reduce ionic diffusion resistance regardless of charge/discharge current density. In addition, the simultaneous presence of Zn and Co ions in the Ni(OH)2 layer improves the efficiency of the active material and reduces the resistance of the unit cell. It was observed that through the effects of the additives in the positive electrode, the asymmetric EC exhibits a high energy density with 35.7 Wh/kg, based on the active material. Furthermore, the energy density decreasing behavior at a high discharge current density was retarded.