The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes. However, many open questions remain when trying to optimize electrolytes and understand solid state battery chemistries.

In this presentation, we will explore the current focus of halide-based ionic conductors in solid state batteries and discuss stability limitations in solid state battery cells at the anode as well as the cathode composites.

In a second part, we show the influence of Si type anode materials on the effective transport and behavior of solid-state batteries

Finally, we will discuss that it is not only important to find fast ionic conductors but that for an effective thermal battery management the thermal transport properties of solid ionic conductors need to be explored and understood. Here we will show the diffusive thermal transport nature of solid electrolytes and their different scaling relations that put in question the assumption of Bruggeman transport in solid state batteries.

Solid polymer electrolytes based on poly(ethylene oxide) (PEO) are of considerable interest in lithium metal batteries. Electrolytes with high modulus are essential for enabling high specific energy batteries with lithium metal anodes [1]. One approach for obtaining high modulus electrolytes is through the use of microphase separated block copolymers comprising a structural block to provide mechanical rigidity (block A) and a soft conducting block to provide avenues for ion transport (block B) [2]. Block copolymers self-assembly into different morphologies such as lamellae, bicontinuous gyroid networks, cylinders arranged on a hexagonal lattice, and spheres arranged on a body-centered-cubic lattice. The ionic conductivity of a block copolymer electrolyte should increase with the volume fraction of the conducting phase. Herein, we explore the impact of several polymers (PS, PMA-POSS, etc.), lithium salts (LiTFSI, POSS-LiTFSI, etc.) and volume fractions of the conducting phase on morphology, mechanical and electrochemical properties of nanostructured block copolymer electrolytes [3,4].

References

1 Soo, P.P; Huang, B.; Jang, Y.; Chiang, Y.M.; Sadoway, D.R.; Mayes. A.M. Rubbery block copolymer electrolytes for solid‐state rechargeable lithium batteries. J. Electrochem. Soc. 1999, 146, 32.

2 Hallinan, D.T.; Villaluenga I.; Balsara N.P. Polymer and Composite Electrolytes. MRS Bulletin, 2018, 43, 759.

3 Sethi, G.; Jiang, X.; Chakraborty, R.D.; Villaluenga, I.; Balsara, N.P. Anomalous Self-Assembly and Ion Transport in Organic-Inorganic Block Copolymer Electrolytes. ACS Macro Letters, 2018, 7, 1056.

4 Villaluenga, I.; Inceoglu, S.; Jiang, X.; Chen,X.C.; Chintapalli, M.; Wang, D.R.; Devaux, D.; Balsara, N.P. Nanostructured Single-Ion-Conducting Hybrid Electrolytes based on Salty Nanoparticles and Block Copolymers. Macromolecules, 2017, 50, 1998.

The possibility of developing practical solid-state batteries (SSBs) has gained momentum in recent years thanks to striking advances at the material level, such as the discovery of new highly-conducting solid-state electrolytes. However, the development of SSBs still faces formidable challenges, such as the integration of the various components, the functionality at full cell level, and the scalability of the fabrication processes.[1] Inorganic solid electrolytes stand out for their high Li-ion conductivity but exhibit drawbacks such as low electrochemical stability (sulfides) or rigidity (oxides, phosphates). Indeed, oxide and phosphate-based electrolytes usually require temperature-assisted densification methods that, when applied to composite cathodes, can induce chemical reactivity among the different cathode components resulting in resistive interfaces and by-products.

In this talk we will discuss our recent work regarding oxide and phosphate-based ion-conductors, including the recent synthesis and characterization of a new form of crystalline LiPON,[2] processing challenges of rigid ceramic materials (in particular regarding high temperature material compatibility in composite cathodes), and low-temperature densification strategies, which in turn allow to shed light into grain-boundary contributions to the total ionic conductivity of the studied materials.

Solid-state batteries pairing a ceramic solid electrolyte with an alkali metal anode promise to improve the safety and energy density of cells. However, cycling solid-state cells at practical current densities in the mA/cm² range can lead to cell failure. While much attention has been devoted to understanding dendrite penetration when plating the anode (charging), the formation of voids when stripping the metal anode (discharging) also has an important role in failure. In this study, stripping of lithium and sodium metal anodes has been investigated as a function of current density, stack-pressure and temperature, revealing the importance of creep in the alkali metal anode on void formation. To explore this, we have used a combination of 3-electrode cells, scanning electron microscopy and X-ray tomography. We show that above a critical current density on stripping, voids will accumulate on cycling at the metal anode/solid electrolyte interface, eventually leading to failure of the cell. It is therefore necessity to strip the metal anode below this limiting current density, as discharging above this critical rate leads to high local currents that can trigger dendrite penetration into the solid electrolyte on subsequent charges. However, we demonstrate that cycling solid-state batteries under moderately elevated stack-pressures and temperatures increases the critical current for voiding by promoting creep in the metal anode, enabling stable discharge at higher rates.

Solid-state batteries with polymer electrolytes (PEs) are at the forefront of candidates to boost energy density and improve the safety of conventional Li-ion batteries. PEs require a wide electrochemical stability window to withstand high-voltage positive electrodes (i.e. LiNi_0.6Mn_0.2Co_0.2O₂, NMC622) and offer stability with the negative electrode (typically Li-metal).¹ However, solid PEs still suffer from low electrochemical stability against highly oxidative and reductive potentials simultaneously. The Double Layer Polymer Electrolyte (DLPE) approach overcomes this issue from the choice of appropriate polymers for the positive electrode and separator respectively, combining them within the same electrochemical device. In this work, polyethylene oxide (PEO), offering stability against Li metal, and polypropylene carbonate (PPC), offering stability at high potentials, were used to prepare DPLE cells with NMC622 and Li-metal electrodes. Nevertheless, the use of a conventional dual-ion conductor lithium-salt (e.g. lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) was found to play a key role on the thermodynamical compatibility between the polymer phases due to ion diffusion from PPC to the more solvating PEO, leading ultimately to cell failure. By modifying the lithium-ion conductive salt we successfully overcome those hurdles and provide guidelines on the design of improved performance cells with DLPE technology.² Ultimately, this allows to assemble cells with high loading NMC622 (1 mAh cm^–2) delivering 160 mAh g^–1 and overcoming the performance of ethylene oxide -based cells, which rapidly degrade in the presence of high cut-off voltage active materials.³ This study provides a detailed understanding on the transport properties and ageing mechanisms taking place in SSLMBs, inspiring further the rational design of new DLPE technology with robust electrochemical performance.

Many efforts in the field of Li-ion batteries are focusing on the development and implementation of solid electrolytes in order to overcome the drawback related to their liquid counterparts such as: flammability, complex encapsulation requirements, high cost and complexity manufacturing processes.  Li-conducting glass-based materials gained attention in the last years as solid state electrolytes for lithium batteries, thanks to their good ionic conductivity at room temperature (10^-3-10^-4 S cm^-1) and their wide electrochemical stability windows.    

In the present work, Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP) glass was 3D-printed by robocasting and stereolitography (SLA) in free-form robust self-standing structures with the main target to obtain 3D batteries with high active area (allowing high specific energy and power per unit volume). The use of 3D printing techniques allowed the fabrication of simple as well as complex architectures, with enhanced contact area with the electrodes. The inks and the printing processes were both optimized in order to reach an accuracy up to ≈100 µm. The printed structures demonstrated an excellent densification after the firing/sintering treatment, as a result of the optimization of the inks formulation, printing process and sintering conditions. Furthermore, ionic conductivity of 3D-printed LAGP electrolyte resulted to be 1.8 10^-4 S cm^-1 at room temperature, in accordance with the values measured on the same material processed with conventional methods. No detrimental reaction products or degradation phenomena were detected by chemical analyses after the sintering.

3D-printed LAGP was successfully cycled in contact with metal-Li. The interface with the anode was previously engineered by depositing 200nm of metallic Ge in order to prevent detrimental reactions between the two materials. A symmetrical cell Li/Ge coated LAGP/Li was successfully cycled for more than 100h.

The successful implementation of 3D printing techniques in LAGP processing represents an innovative approach that will push further the development of all solid state Li-ion batteries with enhanced energy density, thanks to the easy fabrication of 3D structured solid electrolytes.

Self-diffusion in polycrystalline Li1+xTi2-xAlx(PO4)3 (0.2 ≤ x ≤ 0.4) samples followed by 7Li PFG (Pulse Field Gradient) NMR spectroscopy

Isabel Sobrados, Virginia Diez-Gómez, Cristina Ruiz-Santaquiteria, Wilmer Bucheli,

Ricardo Jiménez, Jesús Sanz.

Short and long range lithium motions are discussed in powder Li1+xTi2-xAlx(PO4)3 (LTAP) NASICON compounds prepared by ceramic (x= 0.2 and 0.4) and sol-gel (x= 0.3 and 0.4) routes.

Self-diffusion coefficients were determined with the PFG (pulse field gradient) technique. In these experiments, the stimulated echo π/2-t1-π/2-t2-π/2 sequence was used, in which two field gradient pulses of δ width and g intensity were applied between the two first π/2 pulses and after the third π/2 radiofrequency pulse. From the echo-signal attenuation, induced by the increment of exponent parameters, self-diffusion coefficients (DPFG) were deduced, using the Stejskal and Tanner expression [1]

A(2t1+t2)/A0(2t1+t2)=exp[-ɣ2.g2.δ2.(Δ-δ/3)·DPFG]=exp(-b·DPFG)

where A and A0 stand for echo signal intensity at (2t1+t2) with and without field gradient pulses, ɣ is the nuclear gyro-magnetic ratio, and Δ is the diffusion time used in experiments.

In PFG experiments, time scales differ considerably from those involved in 1/T2 and 1/T1 measurements, however, DPFG values deduced for short Δ times are similar to those deduced by NMR relaxometry. In all analyzed samples, diffusion coefficients measured at short Δ times, are between 5x10-12 and 1x10-11 m2 s-1. At increasing Δ, diffusion coefficients decrease due to restriction. In ceramic LTAP02-C sample, Li diffusion is less restricted than in LTAP04-C sample, where DPFG values increase and the particle size decreases. The analysis of DPFG coefficients in sol-gel LTAP03-SG and LTAP04-SG samples, show strong restriction effects that considerably reduce DPFG values when Δ increases, suggesting that Li diffusion is strongly restricted when the LTAP particles are smaller than 1µm. The restricted diffusion inside NASICON particles is compared to "free" diffusion processes.

From the temperature dependence of conductivity and diffusion coefficients, the activation energy and charge carrier concentrations were determined. In this work, PFG-NMR results show that diffusion coefficients rise with the amount of lithium and temperature.

To reduce restriction effects, denser samples should be prepared. In future works, the PFG technique will permit a better optimization of transport properties in fast ion conductors prepared with different conditions.

1. J.E. Tanner, E.O. Stejskal. J Chemical Physics. 49, 1768- 1777 (1968).

The development of high performance all-solid-state batteries relies on the development of solid electrolytes that have high conductivity, wide chemical, electrochemical and mechanical stability and are easy to process at low temperatures. Halide-type solid electrolytes are a relatively new class of solid electrolytes being studied owing to their compatibility with high voltage cathodes and processability at low temperatures however few structures are known that possess high ionic conductivities within the halide family. Li₂ZrCl₆ is one such material that demonstrates moderate ionic conductivity of 10^-6 S/cm while Cu₂ZrCl₆ exhibits conductivities several orders of magnitude higher. Understanding the factors affecting lithium mobility in A₂ZrCl₆ can aid the design of novel solid-halide electrolytes with tailored frameworks for high ionic conductivity.

In this work, we investigate the composition A₂ZrCl₆ where A is a monovalent cation and the role the A site element has on the crystal structure, ionic conductivity and the associated migration pathways. We demonstrate via long timescale dynamics i.e. kinetic Monte Carlo (KMC) and molecular dynamics (MD) that the A site element does affect the A⁺ ionic conductivity of the material. In general, the more covalent character the A site element possesses the higher ionic conductivity the material exhibits. These results provide a basis to understanding the origin of fast ion transport in solid halide materials.

The solid-state electrolyte field knows a hard competition to provide an ideal composition which needs to fulfill numerous criteria such as, high Li⁺ ionic conductivity, low electronic conductivity, and a high level of mechanical, chemical, electrochemical and air stability as well as interface stability against active electrode materials. Several compositions and chemistries have been investigated, including: oxides, sulfides, halides, polymers; each of them getting their own strengths and weaknesses.^[1]

Dense thin-film solid–state electrolyte separator are interesting to offer (a) a model system to investigate interfaces, and more importantly, (b) a promising pathway to increase the energy density of solid-state cells. The reference of thin-film solid-state electrolyte, for a while, is the lithium phosphate oxynitride LiPON, due to its easy way of deposition/synthesis via reactive RF-Magnetron sputtering. However, LiPON has a ceiling ionic conductivity of ~10^-6 S.cm^-1.^[2]

For a decade, the new family of Lithium Rich Antiperovskite (LiRAP) Li_3-xOH_xHal (Hal = Br,Cl) has been investigated and exhibits low raw material costs, low temperature of synthesis and a bulk ionic conductivity of ~10^-3 S.cm^-1.^[3][4] In addition, previous studies report the possibility to use PVD method to obtain thin layers of the Li₃OCl composition with an acceptable Li+, and electronic conductivity.^[5][6]

Here, we explore different ways to synthesize thin layers of the Li₃OCl solid-state electrolyte by using RF-Magnetron Sputtering or e-Beam with a post annealing treatment. We will presents the structural, chemical and physical characterization, for LiRAP films prepared on glass and platinum coated sapphire substrates, via grazing incident x-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, impedance spectroscopy and chronoamperometry. These findings might accelerate the development of thin film electrolyte as a potential pathway to further increase the energy density of solid-state cells.

In this lecture I discuss a digital twin devoted to the accelerated optimization of the manufacturing process of Lithium Ion Batteries (LIBs). This digital tool is developed by us within the context of the ERC-funded ARTISTIC project.¹ It is supported on a hybrid approach encompassing experimental characterizations, a physics-based multiscale modeling workflow and machine learning models.² Different steps along the LIB cells manufacturing process are simulated, such as the electrode slurry, coating, drying, calendering and electrolyte infiltration. The physics-based modeling workflow encompasses a sequential coupling between Coarse Grained Molecular Dynamics, Discrete Element Method and Lattice Boltzmann Method. It allows predicting the impact of the process parameters on the final electrode microstructure in three dimensions. The predicted electrode microstructures are injected in a performance simulator capturing the influence of the pore networks and spatial location of carbon-binder within the electrodes on the electrochemical response. Machine learning models are used to accelerate the physical models’ parameterization, to mimic their working principles and to unravel manufacturing parameters interdependencies from the physical models’ predictions and experimental data, and for inverse design. The predictive and optimization capabilities of this digital twin, coupling physical models with machine learning models, are illustrated with results for different electrode formulations in the context of LIBs. I also demonstrate the applicability of our approach to Sodium Ion and Solid State Batteries. Finally, the free online battery manufacturing simulation services offered by the project³ to optimize battery electrodes are illustrated through several examples.

Solid-state electrolytes with fast lithium conduction are the core of the all-solid-state Li-battery technology. By substituting the organic electrolyte with a piece of non-flammable ceramic material, we can achieve better safety, higher specific capacity, and a higher energy density. To date, the major bottleneck for this technology is the slow Li diffusion in the solid-state electrolyte and the interfacial incompatibility between the electrolyte and electrodes. To resolve these issues, several families of fast ionic conductors have been developed. Understanding Li diffusion in these materials is essential to the development of novel family fast ionic conductors. To this end, atomistic modeling provides us with a unique tool to obtain comprehensive information on atom motion, which is difficult to access with experimental techniques. In this talk, we showcase our group’s atomistic simulations regarding a novel family of superionic conductors, Li-rich antiperovskites (LiRAPs)

LiRAPs are a promising family of solid electrolytes, which exhibit ionic conductivities above 1 mS/cm at room temperature, among the highest reported values to date. Here, we report on the defect chemistry and the associated lithium transport in Li₃OCl, a prototypical LiRAP, using DFT calculations and classical MD simulations [1]. We studied these materials’ phase, interfacial, and voltage stability [2,3] with DFT, showing good agreement with experiments, further proposing low-dimensional superionic antiperovskites [3]. In addition, the interfacial properties were studied for both protonated and fluorinated materials [4]. Analogous simulations were also carried out for Na-rich antiperovskites [5].

Recent proof-of-concept of electrolytes enabling successful plating and stripping of calcium metal catalyzed research exploring the feasibility of a rechargeable battery technology based on calcium.[1] Estimates of prospective figures of merit at the cell level using open energy-cost models[2] indicate that performances comparable to state-of-the art LIB could be achieved with positive electrodes exhibiting moderate potential (2.5V) and a capacity of 200 mAh/g, and that volumetric energy densities above 1000 Wh/l would be possible considering the same capacity but operation at 3V.

In spite of such nice expectations, the investigation of suitable positive electrode materials has been plagued with a number of hurdles.  On one hand, the lack of standard electrolytes and protocols may result in side reactions inducing misinterpretation of the electrochemical response achieved, which makes real bulk activity difficult to elucidate unless complementary characterization techniques are used. On the other, testing of materials similar to those used in the Li-ion battery field which would enable reversible intercalation/de-intercalation of calcium has to date led to the identification of few active compounds with diverse success.[3] Electrochemical extraction of calcium in some ternary transition metal ions is feasible but the reversibility of the process is more difficult to achieve, which is likely related to strong solvation of calcium ions, with reactions sometimes involving solvent co-intercalation and high cell overpotential.

Overall, there is a long and winding road to follow before reliable proof-of-concept can be achieved and technological prospects evaluated. Development of reliable experimental setups, including reference and counter electrodes, coupled to complementary characterization techniques, as well as computational tools, is mandatory if steady progress is to be achieved.

Solid-state batteries (SSBs) offer the opportunity to leverage energy dense metallic anodes and high voltage cathodes to achieve safe, durable, and affordable secondary energy storage systems^1-3. However, the intrinsic thermodynamic, electrochemical and mechanical instabilities at the buried interfaces limits their performance. Unfavorable electro-chemo-mechanical dynamics can contribute to non-optimal material utilization, mechanical degradation, and poor ion transport. These mechanisms occur at various time- and length- scales and are not fully understood. Lithium metal anodes undergo a lithium deposition reaction which involves the reduction reaction of Li/Li⁺, and a lithium stripping reaction which involves the oxidation of surface Li atoms.  Deposition processes are surface driven mechanisms and have been widely studied in order to understand dendrite formation.  Stripping processes are sub-surface driven mechanisms and involve charge transfer at the interface between lithium and the solid electrolyte (Li|SE). Li stripping can alter the morphology and structure of the lithium metal interface and affect the subsequent deposition process. Non-uniform stripping can lead to sub-surface/interfacial void formation and decrease interfacial contact area between the Li anode and solid electrolyte. Smaller interfacial surface area can lead to high local current densities and decrease the cells threshold for dendrite formation (cell failure). While there are numerous theoretical studies that provide mechanistic hypotheses for pore formation, directly probing lithium stripping is challenging because the phenomena of interest occurs at buried interfaces. Multi-scale characterization of these materials and their electro-chemo-mechanical responses are pivotal towards engineering solid electrolytes for high power and energy applications. Herein, we combine bench top experiments with synchrotron techniques to resolve chemo-mechanics across multiple length scales which impact electrodeposition and dissolution mechanisms (grain, pore, interface).  

Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on ion transport properties is still debated. Here, we focus on Na_{1+ x}Zr₂Si_xP_{3− x}O₁₂ (0≤ x≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on Na-transport properties. Although there is a large body of data available on this NASICON system, transport properties extracted from experiments or theory vary by orders of magnitude, signifying the need to bridge the gap between different studies. Here, more than 2,000 distinct ab initio-based kinetic Monte Carlo simulations have been used to map the statistically vast compositional space of NASICON over an unprecedented time range and spatial resolution and across a range of temperatures. We performed impedance spectroscopy of samples with varying Na compositions revealing that the highest ionic conductivity (~ 0.1 S cm^–1) is achieved in Na_3.4Zr₂Si_2.4P_0.6O₁₂ , in line with our predictions (~ 0.2 S cm^–1). Our predictions indicate that suitably doped NASICON compositions, especially with high silicon content, can achieve high Na⁺ mobilities. Our findings are relevant for the optimization of mixed polyanion solid electrolytes and electrodes, including sulfide-based polyanion frameworks, which are known for their superior ionic conductivities.

Developing high energy density and fast charge/discharge batteries requires new coatings strategies to overcome interfacial impedances between battery cell components. Silicon is a promising anode material for next-generation batteries due to its high volumetric capacity of 2190 mAhl^-1 and low discharge potential of ~ 0.3 V vs Li/Li⁺. In this paper, we report the fabrication, characterisation and electrochemical performance of nano Si electrodes coated with titanicone (TiGL) using a combination of Atomic Layer Deposition (ALD) and Molecular Layer Deposition (MLD). The optimised coated electrode delivers a capacity of 1200 mAhg⁻¹ at 1C for 350 cycles with a capacity retention of 93 % and a high C-rate performance of 150 mAhg⁻¹ at 20C. The improved discharge capacity, efficiencies, rate capability and electrochemical stability are related to enhanced lithium kinetics, stable SEI formation, and better structural integrity of the TiGL coated electrode compared to bare silicon. The use of titanicone as an interface modifier is discussed in the frame of high capacity electrode materials and solid state batteries.

All-solid-state thin-film batteries (TFBs) combine several features of solid-state batteries, such as long lifetime, high charge/discharge rates, and safety with the potential of large-scale manufacturing using physical vapor deposition (PVD) methods. The talk will review several research highlights from our group on how to build an efficient TFB. These include flash-lamp annealing of layered oxide cathodes that enable thin and flexible aluminum foils to be used as conductive substrates [1], engineering a cathode/electrolyte interface with Nb₂O₅ interlayers for a fast ionic transport [2], exploiting ultra-thin amorphous LLZO electrolytes to block lithium dendrites [3], and inserting amorphous carbon interlayers at the Cu/LIiPON interface to facilitate homogeneous Li plating and stripping in an anode-free configuration [4]. At last, we will present the concept of monolithic multi-cell (so-called bipolar) TFBs fabricated with PVD methods, which could resolve the principal handicap of the low specific and areal capacity in TFBs and lead to a new generation of high-power solid-state batteries.

Solid-state batteries offer great potential for large improvements in safety and lifetime, as well as higher energy and power densities. However, the interfacial composition and structure between solid electrolytes and electrode materials often present major deviations from those of the bulk materials. Elucidating the nature of the involved interfaces is required to establish a rational approach towards the successful combination of materials in a new generation of solid-state cells. Controlled interfaces between a solid-state electrolyte, cathode and anode have been realized in 2D-planar and 3D-vertical thin film geometries by applying pulsed laser deposition. The thin film epitaxial model geometries enable full control over the material combination, crystal orientation and elemental termination at all interfaces to explore their evolution during battery operation. Epitaxial engineering is used to realize crystalline thin film model systems, which enables an unique insight into the relation between electrochemistry and structural ordering of the layers and interfaces, not obtainable in conventional polycrystalline battery architectures. Here, I will show the latest results on several different thin film battery architectures, 2D as well as 3D, involving various different cathodes (LiMn2O4, LiCoO2, NMC111, NMC622, NMC811), anodes (Li4Ti5O12, Nb18W16O93) and solid electrolytes (Li0.33La0.57TiO3, Li7La3Zr2O12, Li3PO4).

All-solid-state batteries are seen as next generation energy storage systems and heavily researched worldwide. Within the three major clases of solid electrolytes, oxide-ceramic Li-ion conductors attract significant attention due to their intrinsic safety.  In case of the garnet type Li7La3Zr2O12 (LLZO), the possibility to directly use Li-metal anodes paves the way for high energy densities on cell and battery level. However, the widespread application of such an oxide-based all-solid-state cells depends on the development of scalable synthesis and manufacturing processes while increasing the cell capacity to competitive levels.
While oxides are the most stable solid electrolytes when compared to poylmers or sulfides, there is still some sensitivity to air and protic solvents due to the Li+/H+-exchange. However, with careful tailoring of the manufacturing process due to mechanistic understanding allowed for the development of a new, tailored tape-casting process for LLZO components. 70 µm thick, free-standing LLZO separators can now be fabricated via water based tape casting and all-ceramic free-standing LiCoO2/LLZO mixed cathodes show high active materials utilization. Microstructural engineering by introduction concentration gradients for the active material and the electrolyte allowed to boost discharge capacities to 2.8 mAh cm-2 utilizing 99% of the theoretical capacity. Additionally, the obtained free-standing cathodes have sufficient mechanical stability to allow the application of hybrid and ultra-thin separators to further increase the energy density on the full cell level to industrially relevant levels.

Solid-state lithium metal battery has a huge potential to be a more energy-dense architecture, safety and fast charging capability relative to a current lithium-ion battery. In particular, the cell interface made of oxide-based electrolyte and cathode is believed to withstand more tightly than any other ‘soft’ solid electrolytes (polymer, sulfide electrolytes) once optimized. Sintering at high temperature is generally required to produce dense interfaces for oxide-based electrochemical devices; however, the poor chemical compatibility of the oxide electrolyte with common cathode active materials limits a wide range of material choice, processing and microstructure-performance relationship. Here, potential processing strategies to fabricate oxide-based cathode composite are presented based on an infiltration of LiCoO₂ active material and Li₇La₃Zr₂O₁₂ catholyte through the porous scaffolds or a co-firing of both. Discussion is aimed toward opportunities to meet important target parameters including low interfacial resistance, high-loading capability and specific capacity for high energy and power Li-metal battery.

Solid-state lithium-ion batteries are a promising energy storage solution which promise greater safety with energy and power density comparable to current Li-ion technology. Although many advances have been made recently on the materials level, there still remains a need to understand how the properties of individual parts of the cell (e.g. electrolyte, active material, interfaces) combine to determine device performance on the cell level [1]. Research has focussed on improving solid-state battery performance by tailoring individual properties, such as the electrolyte’s ionic conductivity κ, the cathode active-material conductivity σ, and interface resistances or capacitances. When several materials are brought together to form a porous electrode, the cell performance does not always reflect individual properties in straightforward ways. Optimization of cell designs to achieve satisfactory performance requires an understanding of how the properties of various cell constituents interact. We believe that at this early stage of solid-state battery development, broad and simple design principles are preferable to finely resolved mechanistic models.

To that end, in this work we present a simple model of a planar solid-state battery cell based on the Newman–Tobias theory [2], which illustrates the roles of cathode porosity, interfacial contact, electrolyte ionic conductivity, and active-material electronic conductivity. We show that the current distribution in the porous cathode is governed by a few key dimensionless parameters, including the fraction of the conductivities of the two phases s=σ/(σ+κ) , and the ratio of the kinetic resistance to the bulk resistances. The results show – somewhat counterintuitively – that balancing the bulk conductivities of the interpenetrating cathode phases can lead to improved cell performance, as well as a higher electrode utilization. Insights provided by this approach provide useful guidelines for optimizing solid-state battery design.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is among the cathode materials most discussed for high-performance Li-ion batteries thanks to its capacity of approximately 200 mAh g-1 and its low Co content. Currently, NMC811 is considered for implementation in next-generation electric vehicles, but the high Ni content (> 60 %) still poses challenges, such as oxygen loss at voltages above 4.3 V, impedance rise, transition metal dissolution, and finally, a loss of active lithium in the electrode. These challenges can be mitigated by utilizing appropriate coating and doping strategies and limiting the voltage to standard cycling conditions (2.8 - 3.0 V to 4.3 - 4.5 V). NMC811 can be overlithiated to form Li2NMC811,  in analogy to pure LiNiO2, which can form Li2NiO2 [1]. Such a high lithiation degree increases the initial discharge capacity but leads to a fast voltage loss, especially during the first cycle [2]

In this study, we address two intriguing research questions: (i) Can we control the interface of Ni-rich cathode material with the electrolyte and prevent the formation of detrimental solid electrolyte interphase (ii) Is it possible to take advantage of multi-electron cycling by introducing additional lithium into the host NMC811 structure? To address these questions, Li-rich NMC811 thin-film cathodes were prepared by sputtering from a Li₂O-NMC811 target. Li-rich NMC811 cathodes were tested with LiPON as a solid electrolyte in a thin-film architecture, which offers a simplified 2D model with direct access to the cathode-electrolyte interface. The solid-state electrolyte helped to stabilize the interface and prevented capacity fading, voltage decay, and interface resistance growth. In combination with LiPON, cycling at extended voltage ranges of 1.5-4.7 V was possible without increasing interfacial resistance. It was possible to reversible cycle Li₂NMC811 by lowering the applied potential to 1.5 V. resulting in a discharge capacity of up to 350 mAh g^-1 due to multi-electron cycling. Overall, the all-solid-state cells with a lithium metal anode can cycle in the range of 1.5 V to 4.3 V for 1000 cycles with an average coulombic efficiency of 98.79 %. Our results demonstrate how solid electrolytes that are stable against NMC811 cathodes can unlock the full potential of this Ni-rich cathode class.

Glassy-type solid state electrolytes such as state-of-the-art LiPON avoid grain boundaries and prevent Li-dendrite propagation leading to extremely good cyclability and the commercialization of planar thin-film LiPON-based microbatteries. However, its reduced ionic conductivity (~1 μS/cm) limits its performance at high/discharge rates and the severe degradation of its electrochemical and structural properties upon their exposure to ambient conditions and high temperatures (> 300 ºC) hinders scalability and manufacturability. Among the next generation solid-state electrolytes, NASICON superionic solid electrolyte Li_(1+x)Al_xTi_(2-x)(PO₄)₃ (LATP) with 0.3 ≤ x ≤ 0.5 remains one of the most promising solid electrolytes thanks to its good ionic conductivity (~0.5-1 mS·cm^-1) and outstanding stability in ambient air. Despite the intensive research for bulk systems, there are only very few studies of LATP in thin film form. In particular, the only successful reports of relatively high ionic conduction (~10^-5 S·cm^-1) have been achieved through amorphous sputtered films.

In this talk, we will explore the properties of high performance LATP thin films fabricated by Large-Area Pulsed Laser Deposition. The as-deposited thin films exhibit an ionic conductivity around 0.5 μS·cm^-1 at room temperature (comparable to the state-of-the-art of LiPON) which increases to remarkably high values of 0.1 mS cm^-1 after an additional annealing at 800 ºC. We will discuss the formation of a glassy, intergranular phase connecting highly conducting LATP grains as a possible cause for the significant enhancement in ionic conductivity by two orders of magnitude. The performance of both as-deposited and annealed LATP films makes them suitable as solid electrolytes, which opens the path to a new family of stable and highly performing thin solid-electrolytes. We will discuss its integration with other battery components, with special attention to interfacial coatings matching the electrochemical window at low potentials.

The development of energy storage and conversion devices demanded to generate clean and sustainable energy relies on the design, synthesis, and characterisation of novel materials with suitable properties in terms of ionic or electronic conductivity, ionic insertion capabilities, redox activity, catalytic properties, etc. The structure of the materials used in energy may condition these properties and their overall good performance, and its knowledge is essential for proper understanding and optimising of these materials. To define the crystalline structure, Neutron powder diffraction (NPD) is a powerful tool that, combined with the Rietveld refinement method, is able to provide detailed structural information. This way, properties closely related to the structure and its evolution with external factors (temperature, pressure, cycling in in-operando systems, etc.) can be assessed with greater certainty. Well-known applications of neutron diffraction are the location of oxygen atoms and oxygen vacancies in oxide ion conductors, Li ions in solid electrolytes or Li-ion battery cathodes, protons in fast H⁺ conductors, etc. The ionic conductivity of these diverse materials is partly conditioned by the structure, composition, atomic radii, and formal charges of each atom, among others. An inexpensive and relatively efficient way to exploit these data in order to determine properties such as ionic percolation activation energy is the use of Bond‑Valence Energy Landscape (BVEL), which relies on structural data that can be determined by NPD. In this way, NPD and BVEL form a synergistic tandem that is useful in the assessment of ionic conductors. In this talk, we will present some recent results obtained for different types of energy-related materials, including Li-ion battery electrodes, electrolytes in Na batteries, and H⁺ conductors.

As Li cathode example, an N-doped LiFePO₄-type material, where nitrogen partially replaces an oxygen atom of the olivine tetrahedra lattice at 4c Wyckoff site in the Pnma space group. The structure was correctly determined by the Rietveld method from NPD data, and a subsequent calculation by BVEL confirms the decrease in activation energy (Ea) by about 6 % with respect to the pristine structure upon N-doping. As a solid electrolyte example, collaborative work is presented, in which the structures of Mg-doped NZSP NASICON-type electrolytes were determined at different temperatures from neutron data. A decrease in the activation energy concerning the undoped sample and its temperature dependency is assessed by BVEL. Finally, an example of a proton conductor used as a catalyst is presented, the so-called antimonic acid, where the presence and location of two different H⁺ are verified and identified by means of Fourier density difference maps. In this talk, a brief review of these different materials will be made, with emphasis on the specific structural features determined by the neutrons that explain the desired properties of the materials applied to energy.