Solid-state Cathode Research Articles

Understanding the Phase Evolution and Charging Mechanism in Dual Cation Cathodes

Multivalent batteries offer potential advantages over lithium-ion batteries but face challenges due to limited ionic mobility in solid-state cathodes. Recent investigations have demonstrated that incorporating multivalent cations, particularly calcium ions (Ca2+), into monovalent cathodes such as NaSICON and R-3m NaV2(PO4)3, results in improved capacity retention. This study investigates the phase evolution and charging mechanism in these dual cation cathodes by using a cluster expansion and charge-neutral Monte Carlo simulation in a Ca-Na-V2(PO4)3 system. Our results found that during the discharge with either Ca or Na ions, phase transitions occurs when the oxidation state of the transition metal changes, in particular between Na1V2(PO4)3 - Na3V2(PO4)3 and Na1V2(PO4)3 - Ca1V2(PO4)3. This behavior suggests that the charging pathway of Na/Ca ions can be altered by varying the Ca/Na chemical potential. Figure 1

Operando Investigation on the Role of Densification and Chemo‐Mechanics on Solid‐State Cathodes

AbstractAll solid‐state batteries are desirable for a range of energy storage applications which require high energy density. Achieving a high energy density in a solid‐state battery requires the operation of an energy dense anode with a composite solid‐state cathode. Pores and/or voids within a solid state cathode are ion‐blocking and thus control over the concentration and distribution of pores in the initial electrode and cycled electrode is desirable. This study provides an understanding of the interplay between electrode microstructure and mechanics on active material utilization in solid state cathodes composed of NCM 811 and Li6PS5Cl. Decreasing the solid electrolyte particle size leads to greater active material‐electrolyte contact and less total deformation when exposed to an external load. Composite cathodes with greater compliance can potentially decrease strain between the active material and solid electrolyte, decrease delamination events and result in higher overall active material utilization and high capacity retention.

Light Enables the Cathodic Interface Reaction Reversibility in Solid-State Lithium-Oxygen Batteries.

Limited triple-phase boundaries arising from the accumulation of solid discharge product(s) in solid-state cathodes (SSCs) pose a challenge to high-property solid-state lithium-oxygen batteries (SSLOBs). Light-assisted SSLOBs have been gradually explored as an ingenious system; however, the fundamental mechanisms of the SSCs interface behavior remain unclear. Here, we discovered that light assistance can enhance the fast inner-sphere charge transfer in SSCs and regulate the discharge products with spherical particles generated via the surface growth model. Moreover, the high photoelectron excitation and transportation capabilities of SSCs can retard cathodic catalytic decay by avoiding structural degradation of the cathode with a reduced charge voltage. The light-induced SSLOBs exhibited excellent stability (170 cycles) with a low discharge-charge polarization overpotential (0.27 V). Furthermore, transparent SSLOBs with exceptional flexibility, mechanical stability, and multiform shapes were fabricated for theory-to-practical applications in sunlight-induced batteries. Our study opens new opportunities for the introduction of solar energy into energy storage systems.

Light Enables the Cathodic Interface Reaction Reversibility in Solid‐State Lithium‐Oxygen Batteries

AbstractLimited triple‐phase boundaries arising from the accumulation of solid discharge product(s) in solid‐state cathodes (SSCs) pose a challenge to high‐property solid‐state lithium‐oxygen batteries (SSLOBs). Light‐assisted SSLOBs have been gradually explored as an ingenious system; however, the fundamental mechanisms of the SSCs interface behavior remain unclear. Here, we discovered that light assistance can enhance the fast inner‐sphere charge transfer in SSCs and regulate the discharge products with spherical particles generated via the surface growth model. Moreover, the high photoelectron excitation and transportation capabilities of SSCs can retard cathodic catalytic decay by avoiding structural degradation of the cathode with a reduced charge voltage. The light‐induced SSLOBs exhibited excellent stability (170 cycles) with a low discharge–charge polarization overpotential (0.27 V). Furthermore, transparent SSLOBs with exceptional flexibility, mechanical stability, and multiform shapes were fabricated for theory‐to‐practical applications in sunlight‐induced batteries. Our study opens new opportunities for the introduction of solar energy into energy storage systems.

Efficient Ion Percolating Network for High-Performance All-Solid-State Cathodes.

All-solid-state lithium batteries (ASSLBs) face critical challenges of low cathode loading and poor rate performances, which handicaps their energy/power densities. The widely-accepted aim of high ionic conductivity and low interfacial resistance seems insufficient to overcome these challenges. Here, it is revealed that an efficient ion percolating network in the cathode exerts a more critical influence on the electrochemical performance of ASSLBs. By constructing vertical alignment of Li0.35La0.55TiO3 nanowires (LLTO NWs) in solid-state cathode through magnetic manipulation, the ionic conductivity of the cathode increases twice compared with the cathode consisted of randomly distributed LLTO NWs. The all-solid-state LiFePO4/Li cells using poly(ethylene oxide) as the electrolyte is able to deliver high capacities of 151mAhg-1 (2C) and 100mAhg-1 (5C) at 60°C, and a room-temperature capacity of 108mAhg-1 can be achieved at a charging rate of 2C. Furthermore, the cell can reach a high areal capacity of 3mAhcm-2 even with a practical LFP loading of 20mgcm-2. The universality of this strategy is also presented showing the demonstration in LiNi0.8Co0.1Mn0.1O2 cathodes. This work offers new pathways for designing ASSLBs with improved energy/power densities.

Polycarbonate-Based Solid-Polymer Electrolytes for Solid-State Sodium Batteries.

Solid-polymer electrolytes comprised of polypropylene carbonate (PPC) and varied sodium bis(fluorosulfonyl)imide (NaFSI) salt concentrations are investigated for implementation as a conductive solid polymer electrolyte into solid-state cathode composites utilizing a sodium-layered oxide active material. The ionic conductivity generally increases with NaFSI salt content, reaching ≈1mScm-1 at 80°C at the highest salt concentration (PPC:NaFSI = 0.5:1). Through an all-in-one slurry casting method, Na2/3Ni1/3Mn2/3O2 cathode composites are fabricated in which the dispersed PPC electrolyte acts as the primary binder. Enabled by a bilayer polymer electrolyte system, cycling performance with the PPC cathode electrolyte is optimized with respect to salt concentration and anode material. The best cyclability is achieved with a moderate salt concentration electrolyte (PPC:NaFSI = 5:1), showcasing an initial capacity of 83mAhg-1 with a remarkable 80% capacity retention after 150 cycles at C/5 rate and 60°C. The superior performance of the lower salt concentration electrolyte is attributed to better electrochemical stability, as confirmed by linear sweep voltammetry and online electrochemical mass spectrometry measurements. These results underscore the potential of carbonate-based polymer electrolytes and the importance of balancing electrolyte conductivity and stability in cell design.

Quantifying the Thermochemistry of Kinetic Transitions in a Solid-State Charged Li/Llzo/LCO Cell Using Differential Scanning Calorimetry

It is a general understanding that removal of combustible organic solvent with the introduction of solid-state electrolytes would make a battery safer. However, safety in solid state batteries is multifaceted and involves analysis of self-heating rates, total generated energy, thermal runaway onset temperature, maximum temperature, and thermal runaway prevention mechanisms1,2. The use of reactive lithium metal as the anode, and cathode material such as LiCoO2 that releases O2 when heated in its delithiated state, results in conditions in which the exothermic reaction 4Li+O2→2Li2O may occur if these reactants come into contact. We measure heat flow data using a differential scanning calorimeter (DSC) and hermetically sealed DSC pans to establish a reaction thermochemistry responsible for self-heating of LixCoO2|LLZO|Li metal cell, with x=0.43 (which corresponds to 4.3V vs. Li). While the main exothermic reaction is 4Li+O2→2Li2O when only Li0.43CoO2 is present in the cathode3, a practical solid-state cathode will almost certainly contain conductive carbon and a fluorinated binder. We carry out careful DSC analysis with a range of components and ratios of components to quantify the expected reaction pathway, and amount of heat released, for a cathode that contains Li0.43CoO2, carbon additive, and PVDF binder. We find that the carbon and PVDF strongly influence the reaction pathway upon heating to 500°C in our DSC experiments. Hence, the presence of even small weight fraction components in a solid-state cathode should be considered when evaluating their thermochemistry upon heating.

Mechanistic Underpinnings of Heterogeneities in Solid-State Battery Cathode

Solid-state batteries (SSBs) are regarded as the potential candidate for next-generation energy storage systems due to their enhanced energy density and safety characteristics. However, realizing the true potential of the SSBs is predicated on addressing several interfacial and mechanistic challenges stemming from the mechanically rigid nature of the solid electrolyte (SE). In this regard, the presence of solid-solid point contacts within the solid-state cathode poses a critical bottleneck. Point contacts not only result in transport and kinetic limitations but also lead to stress hotspots within the composite cathode. Moreover, microstructural heterogeneities govern the spatial variability of these point contacts, thereby influencing the coupled electrochemical, thermal, and mechanical signatures. Thus, understanding the critical role of cathode microstructural heterogeneity in dictating the mesoscale interactions and its implications on the SSB performance is necessary. In this work, mechanistic underpinnings of heterogeneities in solid-state cathode will be studied and its implications on the coupled electrochemical-thermal-mechanical response of SSBs will be delineated. Lastly, the effect of cathode architecture will be explored towards achieving high energy density SSBs.

Inorganic Ultra-Rich Solid Composite Electrolytes for High-Voltage Solid-State Batteries

Solid-state batteries (SSB), in which flammable organic liquid electrolytes are replaced by inherently safer solid electrolytes (SEs), are considered to be the evolution of current Li-ion battery technology toward greater safety and higher energy density. Among the various SEs, the PEO-LiTFSI system has been the most studied due to its low cost and ease of processing. However, the relatively low oxidation stability of PEO-LiTFSI at about 4.0 V vs. Li/Li+ does not allow the use of high-voltage cathode active materials, which limits the available energy density [1]. We propose that a high content of Li-ion conductive ceramic in the PEO-LiTFSI matrix increases oxidation stability, allowing stable cell cycling with Ni-rich NMC cathode at higher voltages. This class of inorganic ultra-rich composite SEs has attracted much interest recently [2, 3].In this work, we present a self-standing, dense, flexible (Fig.1a), and thermally stable (Fig.1b) composite solid electrolyte (INURSE 30) that has an ultra-high content of Li-ion conductive LLZO (90 wt%, as confirmed by TGA in Fig. 1b)in the PEO-LiTFSI matrix. The ionic conductivity of INURSE 30 is 1.4x10-5 S/cm at 60ºC. The INURSE 30 electrolyte shows long-term cycling stability of more than 2000 h at a current density of 0.01 mA/cm2 in symmetric cells with Li electrodes. In addition, the high-voltage stability of INURSE 30 was demonstrated in solid-state cells with a composite solid-state cathode containing 75 wt% NMC622 and a Li metal anode. The Li/INURSE 30/NMC622 coin cell shows good coulombic efficiency and capacity retention, as shown in Fig.1c. K.V. acknowledges the financial support from Fundacíon CIDETEC and DESTINY PhD programme which received funding from the European Union's Horizon2020 research and innovation programme under the Marie Skłodowska-Curie Actions COFUND - Grant Agreement No: 945357.

(Keynote) Heterogeneities in Solid-State Battery Interfaces and Architectures

While lithium-ion batteries have garnered significant success over the past decades, the development of next-generation batteries with higher energy densities is crucial for future electromobility demands such as long-range electric vehicles and electric aviation. In this context, solid-state batteries (SSBs), consisting of an inorganic solid electrolyte and lithium metal, are promising in simultaneously improving the energy density and safety. Despite their irrefutable promise, the realization of practical SSBs is predicated on overcoming important challenges pertaining to electro-chemo-mechanics, transport, and interface evolution. Myriad heterogeneities ranging from defects/voids at the lithium/solid electrolyte interface, grain boundaries in the solid electrolyte and singularities in the solid-state cathode have a pivotal influence on the onset of failure and electrochemical performance. In this presentation, the critical role of heterogeneities on the mechanistic interplay at solid-solid interfaces and the underlying failure mechanisms will be delineated. Governed by the manifestation of spatio-temporal heterogeneity at scales, the origin of solid/solid interface instability, resultant asymmetry in the plating/stripping response and electrode crosstalk implications will be discussed.

Direct electrochemical extraction of metallic Li from a molecular liquid–Based electrolyte under ambient conditions

The high chemical activity of metallic Li hinders its efficient electrochemical extraction at low temperatures, necessitating the use of energy- and cost-intensive methods such as vacuum thermal reduction or electrodeposition from ionic-liquid and molten-salt electrolytes. Herein, we report the direct room-temperature electrowinning of metallic Li from a simple low-cost electrolyte, namely a solution of LiCl in dimethylacetamide (DMAc), determine the optimal concentration of LiCl, and examine the redox processes in the optimized system. Potentiostatic deposition on high-purity Al is shown to induce solid-state cathode alloying and thus produce a uniform, flat, and dense coating of a LiAl master alloy comprising spherical clusters formed by LiAl alloy nanosheets. Finally, the direct smelting of electrodeposited films is proposed as a method of rapidly realizing the “thin film” to “bulk” transformation of electrodeposited materials to stabilize metallic Li and form bulk Li-based alloys. Thus, this study provides a basis for the continuous, low-cost, sustainable, and fast electrochemical production of bulk active metals or their alloys.

Stable cycling of high-density three-dimensional sintered LiCoO2 plate cathodes

High-density sintered plate-type cathodes composed of only an active material can achieve a high energy density of lithium-ion batteries (LIBs) beyond the current state of the art. However, slow lithium ion movement in the solid-state cathode plate and deterioration of the grain boundary of sintered cathodes over many charge/discharge cycles are obstacles to commercialization. Herein, we present a new three-dimensional high-density sintered LiCoO2 plate cathode with periodically aligned channels, which enable fast charging/discharging of high-energy-density LIBs. In addition, we investigate the grain-boundary cracking mechanism and introduce a conductive coating agent to LiCoO2 cathodes that prevents crack propagation, enhances electron transfer between sintered LiCoO2 grains, and prevents the formation of an undesirable cathode electrolyte interphase. In full-cell experiments, the cell with a sintered LiCoO2 cathode with industrial-level current density (3.5 mA cm−2) has a volumetric capacity (723 mAh cm−3) 21% higher than that of a conventional cathode (597 mAh cm−3). The cathode coated with the conductive agent shows a 30% higher cycle life after testing for 500 cycles compared to the bare cathode. High-density sintered cathodes are fabricated with an industrially acceptable cycle lifetime of 84% capacity retention over 500 cycles at 1 C.

Chemo-Mechanics in All Solid State Composite Cathodes

Decarbonization of transportation systems will require a suite of battery technologies depending on the mode and scale. Solid state batteries are an energy dense and non-flammable alternative to conventional batteries and is currently being explored for passenger vehicles and portable electronics1,2. While there is considerable interest in understanding lithium metal anodes for solid state batteries, many significant challenges still exist in solid state cathodes. Solid state cathodes are composites and usually include a combination of active material, solid electrolyte and binder3. The composition, microstructure, and properties of the cathode has significant implications for rate performance, energy density, and lifetime of these systems. Here we examine composite solid state cathodes comprised of argyrodite Li6PS5Cl and LiNi0.8Co0.1Mn0.1O2. We examine how composition and structure influences performance with a specific lens on understanding how chemo-mechanical transformations and buried solid-solid interfaces evolved during cycle operation. In addition we show how external operating conditions (temperature/pressure) influence stress generation in these systems. In this talk we will discuss how we combine novel bench-top experiments with advanced operando x-ray characterization tools to quantify stress and correlate it to structure.[1]Shen, F., Dixit, M. B., Zaman, W., Hortance, N., Rogers, B., & Hatzell, K. B. (2019). Composite electrode ink formulation for all solid-state batteries. Journal of The Electrochemical Society, 166(14), A3182.[2]Hatzell, K. B., & Zheng, Y. (2021). Prospects on large-scale manufacturing of solid state batteries. MRS Energy & Sustainability, 8(1), 33-39.[3]Ren, Y., Hortance, N., & Hatzell, K. (2022). Mitigating Chemo-Mechanical Failure in Li-S Solid State Batteries with Compliant Cathodes. Journal of The Electrochemical Society.

Development of Large Area All Solid-State Lithium-Ion Cells Using Scalable and Manufacturable Coating Processes

The NREL team has fabricated all solid-state full cells with sulfide-based electrolytes using fabrication techniques suitable for high speed/low-cost manufacturing, such as slurry and tape casting. Slurry coating is a well-established and cost-effective process feasible for large scale/continuous process (e.g., roll-to-roll processing). However, most solid-state cells fabricated to date have been small area (1 cm2) cells with single mAh capacities. These cells are generally fabricated by dry mixing of powders and compressing layers to hundreds of MPa up to GPa of pressure and high temperatures to condense powders into a coin-cell size battery. The use of such high pressures is not suitable for large-scale manufacturing. Further, the separator layer in this configuration is often prohibitively thick (hundreds of microns) resulting in poor rate capability and low energy density. NREL has demonstrated ability to cast thin (100 micron) electrically isolating sulfide-based separator layers and composite solid-state cathodes. Functioning large-area cells (30 cm2) have been fabricated by punching out sections of cast layers to make cells tested at modest pressures. The chemical reactivity of sulfide-based electrolytes with solvents for casting and active cathode oxide materials (NMC, NCA, etc.) is particularly challenging. Figure below shows all solid-state cathode (left) and anode/argyrodite separator (right) having dimensions of 5X6 cm. The anode, cathode, and separator all use a chloride argyrodite electrolyte (Li6PS5Cl). The anode active material is graphite and cathode is alumina coated NMA with high specific capacity (> 200 mAh/g). Initial performance testing will be shared. Figure 1

(Digital Presentation) Conceptual Design of Oxide-Based Solid-State Li-Battery for Urban Air Mobility

In metropolitan areas, traffic congestion and pollution are serious challenges due to the continuous rapid growth in the number of vehicles and population. These concerns have prompted a global trend toward the electrification of transportation powertrains. Electric vertical take-off and landing (eVTOL) aircraft is an efficient and safe alternative mode of transportation with a significant impact on urban mobility, which attracts considerable attention [1]. It could avoid traffic on the ground and allow people to commute between two locations in less time while requiring no additional run-up space. Nevertheless, one of the main challenges with such aircraft is to provide electrical storage systems, such as batteries, which are safe, efficient, reliable, and capable of producing the energy and power demand to meet mission requirements [2].High flammability and risk of thermal runaway in current Li-ion batteries motivate to develop next-generation chemistries such as all-solid-state batteries (ASSB) as alternative electrical storage systems for eVTOL. However, ASSB currently suffer from low solid electrolyte conductivity, as well as non-utilised active material, and significant reaction overpotentials due to a small effective active area [3]. Electrode composition and structure have a crucial impact on three performance-relevant microstructure parameters, i.e. effective active area, effective ionic conductivity, and effective electronic conductivity. However, considering these restrictions experimentally by producing and evaluating a wide range of design parameters to achieve a well-performing design for ASSB is both time- and resource-intensive. To address these issues, we conduct model-based structure evaluation. Here, we extend the P2D model with a microstructure surrogate model based on Laue's work [4] for Li-ASSB (see Fig. 1-a), because electrode microstructure is important for the effective parameters. Further, this link between the P2D model and microstructure modelling could provide a better understanding of the electrode structure and especially the effects of percolation, which cannot be properly covered by classical Bruggeman approaches. This model is then incorporated into a global optimisation algorithm to determine the optimal design of solid-state cathode with respect to eVTOL power demand. Finally, we compare the performance of the battery at the identified optimal electrode design, electrode reference design, and electrode design with that of the Bruggeman approach. Based on our prior research, we identified that hybrid electrolytes with 12.7 vol% LLZTO had the best performance among other types of hybrid electrolytes at a relatively high C-rate, i.e. 1C. Therefore, we employed this electrolyte for the modelling of Li-ASSB for eVTOL application [5].Fig. 1-b shows an exemplary result from a simpler model without percolation, i.e. Bruggemann approach, and a microstructure surrogate model. As can be observed, taking into account a more realistic structure in the electrode, the ASSB could only meet 32% of the mission requirements. However, optimisation of solid-state cathode structure significantly increases flight time in comparison to the reference electrode.In summary, we could show that future electrification of transportation powertrains will necessitate optimisation of the solid-state electrode structure and composition in order to meet the high demands for energy and power density. Also, our work highlights the urgent need to consider microstructure physical effects at an early stage of design for a realistic sizing of batteries. References Jain et.al., Proc. 4th Int. Conf. Electron. Commun. Aerosp. Technol. (2020) 1173–1178Donateo et.al., Aerospace 7, no. 5 (2020): 56Bielefeld et.al., The Journal of Physical Chemistry C 123, no. 3 (2018): 1626-1634Laue et.al., Energy Technology, 8(2) (2020): 1801049Toghyani, et.al., J. Electrochem. Soc (2022). Figure 1

Unconventional Charge Transport in MgCr2O4 and Implications for Battery Intercalation Hosts.

Ion transport in solid-state cathode materials prescribes a fundamental limit to the rates batteries can operate; therefore, an accurate understanding of ion transport is a critical missing piece to enable new battery technologies, such as magnesium batteries. Based on our conventional understanding of lithium-ion materials, MgCr2O4 is a promising magnesium-ion cathode material given its high capacity, high voltage against an Mg anode, and acceptable computed diffusion barriers. Electrochemical examinations of MgCr2O4, however, reveal significant energetic limitations. Motivated by these disparate observations; herein, we examine long-range ion transport by electrically polarizing dense pellets of MgCr2O4. Our conventional understanding of ion transport in battery cathode materials, e.g., Nernst-Einstein conduction, cannot explain the measured response since it neglects frictional interactions between mobile species and their nonideal free energies. We propose an extended theory that incorporates these interactions and reduces to the Nernst-Einstein conduction under dilute conditions. This theory describes the measured response, and we report the first study of long-range ion transport behavior in MgCr2O4. We conclusively show that the Mg chemical diffusivity is comparable to lithium-ion electrode materials, whereas the total conductivity is rate-limiting. Given these differences, energy storage in MgCr2O4 is limited by particle-scale voltage drops, unlike lithium-ion particles that are limited by concentration gradients. Future materials design efforts should consider the interspecies interactions described in this extended theory, particularly with respect to multivalent-ion systems and their resultant effects on continuum transport properties.

Fabrication and Performance of Li-S/Se Solid State Cathodes with Holey Graphene As a Conductive Scaffold and Binder

Electric aircraft demonstrate potential as the future of aviation, offering zero emissions, lower noise, and potentially lower operational costs than aircraft powered by internal combustion engines. Currently, state-of-the-art lithium (Li) ion batteries used to enable today’s electrical vehicles lack the specific energy (< 250 Wh/kg) required to make electric flight (ideally requiring >400 Wh/kg) an economically beneficial endeavor. Additionally, Li ion batteries introduce serious safety concerns due to the highly flammable organic liquid electrolytes contained within the cell. Li-sulfur/selenium (Li-S/Se) cell chemistries possess high theoretical energy densities (2600 and 1160 Wh/kg, respectively) and therefore are a promising option to power electric aircraft. Rings of S doped with Se as the active cathode material result in a cell electrochemistry that can provide a balanced energy and power output during their reaction with Li. To improve safety, the S/Se cathode can be implemented with a solid-state electrolyte (SSE) to ensure the batteries would not be flammable. However, there are tremendous challenges in optimizing the interface between SSEs and the active material in the cathode composite to achieve desirable performance. In this presentation, we report our findings on the cathode fabrication and performance for solid-state Li-S/Se battery cells. We demonstrate that holey graphene (hG), a structural derivative of graphene, can serve as a scaffold host and binder to facilitate the close contact between the active material and SSEs. In addition, hG has unique properties such as through plane holes and dry compressibility that can aid in the fabrication and electrochemical performance of these high energy density solid-state batteries.

Constructing Favorable Microstructures in Solid-State Organic Cathodes Via Mechanical Property Manipulation

Organic electrode materials, due to their low environment footprint and high material-level specific capacities, have become competitive alternatives to inorganic materials for solid-state batteries (SSB) in recent years. Additionally, the soft nature of organic compounds ensures consistent and intimate contact with solid sulfide electrolytes during cycling, which is beneficial for battery longevity. However, the low-modulus organic materials and high-modulus sulfide electrolytes, upon mixing and compression, would form unfavorable composite microstructure where sulfide particles are encapsulated by organics and cannot form an efficient ion conduction path. This mismatch in mechanical property prevents a high fraction of organic compounds to be used in a solid-state cathode, limiting the energy density of organic solid-state batteries.Here we report the formation of favorable microstructures of organic cathodes by “softening” the sulfide electrolytes. Solvent treatment of the sulfide electrolyte Li6PS5Cl more than halves its modulus from 28.6 ± 8.5 GPa to 16.0 ± 1.6 GPa. Thermal gravimetric analysis, Raman spectroscopy, and X-ray diffraction were used to elucidate the evolution of the sulfide electrolyte during the softening and recovering process. The organic cathode formed by mixing organic materials with this softened electrolyte shows a favorable microstructure where the electrolyte forms a percolated domain. As a result, the utilization of an organic material, pyrene-4,5,9,10-tetraone (PTO), is increased by 133.6% and 90.8% compared with cells with a re-hardened and the pristine Li6PS5Cl, respectively. The mass fraction of PTO can be improved from 20 to 40wt% while maintaining high utilization (85.7%). Our exploration of softened electrolyte builds the correlation among structure, mechanical property, microstructure engineering and battery performance, and the strategy is applicable to other active materials with low modulus.

(Invited, Digital Presentation) Heterogeneities at Solid/Solid Interfaces

Solid-state lithium metal batteries hold the potential to enhance the energy density, power density and safety of conventional lithium-ion batteries. Interface stability and performance of solid-state batteries is predicated on the coupled set of electrochemical-mechanical-transport interactions that underlie the solid-solid interfaces within the system. Microstructure of the solid-state cathode dictates the distribution of percolation pathways, reaction kinetics and evolution of distinct internal resistance modes. Morphological response of the anode-electrolyte interface is influenced by various aspects including the presence of defects, grain boundaries and mechanical/transport properties of the solid electrolyte and lithium. In this presentation, the mechanistic role of heterogeneities on the morphological stability of the anode, onset of mechanical/thermal hot spots and electrochemical response of the cathode will be analyzed. The implications of heterogeneous kinetic-transport interactions and chemo-mechanics interplay on the performance and failure modes in solid-state batteries will be delineated.

Kinetics or Transport: Whither Goes the Solid-State Battery Cathode?

Solid-state batteries (SSBs) hold the potential to enhance the energy density, power density, and safety of conventional lithium-ion batteries. The theoretical promise of SSBs is predicated on the mechanistic design and comprehensive analysis of various solid-solid interfaces and microstructural features within the system. The spatial arrangement and composition of constituent phases (e.g., active material, solid electrolyte, binder) in the solid-state cathode dictate critical characteristics such as solid-solid point contacts or singularities within the microstructure and percolation pathways for ionic/electronic transport. In this work, we present a comprehensive mesoscale discourse to interrogate the underlying microstructure-coupled kinetic-transport interplay and concomitant modes of resistances that evolve during electrochemical operation of SSBs. Based on a hierarchical physics-based analysis, the mechanistic implications of solid-solid point contact distribution and intrinsic transport pathways on the kinetic heterogeneity is established. Toward designing high-energy-density SSB systems, the fundamental correlation between active material loading, electrode thickness and electrochemical response has been delineated. We examine the paradigm of carbon-binder free cathodes and identify design criteria that can facilitate enhanced performance with such electrode configurations. A mechanistic design map highlighting the dichotomy in kinetic and ionic/electronic transport limitations that manifest at various SSB cathode microstructural regimes is established.