The global transition to sustainable energy systems requires breakthroughs in electrochemical storage technologies that are not only safe but also resource efficient. Solid-state batteries (SSBs), which use superionic solid electrolytes (SEs) instead of flammable liquid electrolytes, are at the forefront of this transformation. In general, SEs promise increased safety, access to high-voltage cathode and metal anode chemistries, and new avenues for circular design and recyclability. However, to reach their full potential, intertwined challenges related to ion transport, (electro)chemical stability, manufacturing, processing, and cost must be overcome. This 2026 roadmap on next-generation SEs for battery applications outlines new directions that will contribute to research in the field of SSBs over the next decade. It provides an overview of the current state of the art in sulfide- and halide-based SEs for Li and Na systems, examines post-Li/Na chemistries (K, Mg, and others), and highlights advances in hydroborate, fully reduced (irreducible), and compositionally complex (high-entropy) electrolytes, as well as glass-ceramic electrolytes. Beyond material innovation, the paper emphasizes the critical role of redox activity in SEs, scalable processing, high-throughput synthesis, and machine learning, as well as operando analytics and nuclear magnetic resonance spectroscopy to accelerate discoveries and gain a better understanding of structure–property relationships. Finally, the growing importance of recycling and circular design for ensuring sustainability is highlighted. By combining insights from chemistry, materials science, data (computational) science, and manufacturing, this article assumes that future SEs will progressively evolve from passive components to active design elements in high-energy-density electrochemical systems. The integration of multidisciplinary innovations will be crucial to realizing the potential of SSBs in practical technologies that power a decarbonized world.

In order to increase the industrial appeal of solid-state batteries (SSBs) based on garnet Li₇La₃Zr₂O₁₂ (LLZO), the possibility of manufacturing them using scalable production processes such as tape casting must be demonstrated. In particular, the scalable production of thick, high-capacity oxide-ceramic composite cathodes based on Ni-rich LiNi_xMn_yCo_zO₂ (NMC) remains a key challenge on the path to realizing ceramic SSBs with competitive energy densities. The limited thermal compatibility between NMC and LLZO during sintering requires the use of a sintering aid such as Li₃BO₃ (LBO), which, however, impairs the rheological stability of tape casting slurries. In this work, we have developed a new tape-casting process for thick oxide-ceramic composite cathodes by establishing a slurry formulation that is compatible with multiphase cathode compositions and enables the reproducible fabrication of composite NMC cathode tapes with high active material loading. Two cathode configurations are investigated: NMC-LLZO-LBO composite cathodes, where LLZO serves as the catholyte, and LLZO-free NMC-LBO cathodes. After cosintering, the residual porosity of the ceramic cathodes is infiltrated with a polymer electrolyte with and without conductive carbon additives to form hybrid polymer-ceramic SSBs. By systematically correlating cathode chemistry, secondary phase formation, and electrochemical performance, this study demonstrates how cathode chemistry and the balance between ionic and electronic transport pathways influence capacity utilization and cycle stability in thick, tape-cast NMC-based composite cathodes.

Next-generation rechargeable batteries require materials that offer enhanced electrochemical capabilities. Achieving these goals depends on understanding the fundamental principles governing these materials, which presents challenges associated to the complex interactions between composition, structural characteristics and electrochemical performance in battery materials. Despite intensive research, progress remains limited regarding effective strategies to mitigate the degradation of fragile alkali-metal-deficient frameworks arising from lattice stress and structural or chemo-mechanical instability upon cycling. In this Review, we explore the importance of chemical heterogeneity in rechargeable battery materials. We discuss how heterogeneity at atomic scale, nano-domains and up to phase-segregated levels within particles can enhance the electrochemical properties of battery materials beyond those of their homogeneous counterparts. Introducing chemical heterogeneity, principles and mechanisms can be unlocked to develop materials with improved structural stability, ion conductivity, redox activity, and phase transition characteristics, driving progress in battery technology. Finally, we outline the challenges and strategies for developing the future battery materials. (Figure presented.)

All-solid-state batteries have great potential to outperform conventional lithium-ion batteries in both safety and energy density, as the solid electrolyte can potentially accommodate high-energy-density anodes such as metallic lithium or silicon more safely. However, the high-valence cations present in most highly conductive solid electrolytes facilitate reductive decomposition at low potentials, leading to significant irreversible lithium inventory loss. Preventing this requires the development of solid electrolytes that are thermodynamically stable at low operating potentials while providing high ionic conductivity and sufficient oxidative stability. To realize this, we explored a new family of Li-rich antifluorite irreducible solid electrolytes, Li2.65S0.35NxP0.65–x, the first reported nitrido-phosphido-sulfide, and investigated their application in all-solid-state batteries. The optimized composition Li2.65S0.35N0.15P0.5 possesses a remarkably high ionic conductivity of 1.05 mS cm–1, as well as a relatively high oxidative stability of 1.15 V vs Li+/Li for this class of materials. Ab initio molecular dynamics and density functional theory simulations reveal that enhanced Li diffusion is the result of enlarged diffusion bottleneck sizes. These are a consequence of (i) substitution with smaller anions or (ii) increased electrostatic repulsion from the substitution with high-valence anions. Importantly, the oxidative stability makes Li2.65S0.35N0.15P0.5 exhibit good compatibility with Si anodes, and in conjunction with the high ionic conductivity, this enables a high initial Coulombic efficiency of 94.2% as well as a stable cycle life of a full cell with a micron silicon–Li2.65S0.35N0.15P0.5 anode and a LiCoO2–Li3InCl6 cathode. This work highlights the potential of irreducible solid electrolytes for the design of all-solid-state batteries with low-potential and high-energy-density anodes.

Solid-state batteries currently receive extensive attention due to their potential to outperform lithium-ion batteries in terms of energy density when featuring next-generation anodes such as lithium metal or silicon. However, most highly conducting solid electrolytes decompose at the low operating voltages of next-generation anodes leading to irreversible lithium loss and increased cell resistance. Such performance losses may be prevented by designing electrolytes which are thermodynamically stable at low operating voltages (anolytes). Here, we report on the discovery of a new family of irreducible (i.e., fully reduced) electrolytes by mechanochemically dissolving lithium nitride into the Li₂S antifluorite structure, yielding highly conducting crystalline Li_2+xS_1-xN_x phases reaching >0.2 mS cm^-1 at ambient temperature. Combining impedance spectroscopy experiments and ab initio density functional theory calculations we clarify the mechanism by which the disordering of the sulfide and nitride ions in the anion sublattice boosts ionic conductivity in Li_2+xS_1-xN_x phases by a factor 10⁵ compared to the Li₂S host structure. This advance is achieved through a novel theoretical framework, leveraging percolation analysis with local-environment-specific activation energies and is widely applicable to disordered ion conductors. The same methodology allows us to rationalize how increasing nitrogen content in Li_2+xS_1-xN_x antifluorite-like samples leads to both increased ionic conductivity and lower conductivity-activation energy. These findings pave the way to understanding disordered solid electrolytes and eliminating decomposition-induced performance losses on the anode side in solid-state batteries.

One of the major challenges in advancing polymer-inorganic hybrid solid electrolytes (HSEs) lies in comprehending and controlling their internal structure. In addition, the intricate interplay between multiple phases further complicates efforts to establish the structure-property relationships. In this study, by introducing a multifunctional LiI additive to an HSE compromising of polyethylene oxide (PEO) polymeric electrolyte and the fast lithium-ion conductor Li₆PS₅Cl, the relationship between the bulk and interface structure and ascertaining their impact on lithium-ion dynamics within the HSE is disentangled. Using multidimensional solid-state nuclear magnetic resonance, we find that the addition of LiI stabilizes the internal interfaces and enhances lithium-ion mobility. A kinetically stable solid-electrolyte interphase is formed at the lithium-metal anode, increasing the critical current density to 1.3 mA cm⁻², and enabling long-term stable cycling of lithium symmetric cells (>1200 h). This work sheds light on tailoring the structure of HSEs to improve their conductivity and stability for enabling all-solid-state lithium-metal batteries.

Fluorination of electrolytes has been a widely used strategy to enable stable cycling in lithium metal batteries. However, a move toward fluorine-free electrolytes is desirable given the safety and environmental concerns surrounding fluorinated materials. Designing these electrolytes requires a comprehensive understanding of bulk electrolyte and interfacial properties in the absence of fluorine, particularly the solvation structures surrounding Li⁺ and the solid electrolyte interface (SEI) composition. Among fluorine-free Li salts, lithium nitrate (LiNO₃) is often used to obtain highly ion-conductive SEI components. However, its poor ion dissociation and rapid consumption upon freshly plated lithium currently hinder its use as the main electrolyte salt. Herein, we show that the modification of Li⁺ inner solvation structures by employing lithium bis(oxalato)borate (LiBOB) as the secondary salt in LiNO₃/diglyme electrolytes synergistically improves both bulk Li⁺ transport and SEI properties. It significantly enhances ion dissociation, which increases the ionic conductivity of the electrolyte despite an increase in its viscosity. Furthermore, the presence of LiBOB-derived outer SEI components over the LiNO₃-derived ion-conductive inner SEI layer results in low-surface-area Li deposits and lower Li⁺/anion consumption during cycling. The dual-salt fluorine-free electrolyte enables stable, long-term cycling in Li/Cu cells for >700 cycles and shows promising capacity retention in Li/LFP full cells at ambient temperature. Our work highlights the importance of tuning the Li⁺ solvation structures for optimizing bulk and interface properties in fluorine-free electrolytes and presents a viable pathway toward the development of greener electrolytes for lithium metal batteries.

Irreducible solid electrolytes (SEs), characterized by non-Li framework ions in their lowest oxidation states, offer intrinsic compatibility with low-reduction-potential, high-capacity negative electrodes, such as lithium metal and silicon. In these SE materials, disorder engineering and vacancy formation reduce lithium-ion diffusion barriers, achieving room-temperature ionic conductivities exceeding 0.1 mS cm^–1. Experiments and atomistic simulations confirm that irreducible SEs form decomposition-free interfaces with Li metal. Their limited oxidative stability can be addressed by pairing them with an electrolyte layer stable with practical cathodes yet demanding interface compatibility between the two electrolyte layers. Here we highlight key research directions to accelerate irreducible SE transition from laboratory to practical application, including expanding compositional diversity, optimizing interfaces with cathode-facing electrolytes, developing scalable thin-film processing, and exploring compatibility with other low working potential anodes like silicon. Addressing these challenges is essential to unlock the full potential of irreducible SEs for high-energy, long-life, all-solid-state batteries.

By varying the bromine content and cooling method, we are able to induce site disorder in the Li_6-xPS_5-xBr_1+x (x = 0, 0.3, 0.5) system via two routes, allowing us to disentangle the impact of site disorder and chemical composition on conductivity. Through solid-state nuclear magnetic resonance (NMR), we can explore the chemical environment as well as short-range lithium-ion dynamics and compare these to results obtained from neutron diffraction and electrochemical impedance spectroscopy (EIS). We find that the cooling method has a profound effect on the ⁷Li and ³¹P environment that cannot be explained through 4d site disorder alone. The configurational entropy (S_conf) is used as a more complete descriptor of structural disorder and linked to distortions in both the phosphorus and lithium environment. These distortions are correlated to increased intercage movement through ⁷Li T₁ spin-lattice relaxation (SLR) NMR. Further analysis of the prefactors obtained from SLR NMR and EIS allows us to obtain the migrational entropy (ΔS_m). For short-range SLR movement, the ΔS_m correlates well with S_conf, implying that increased intercage movement is related to distortion of the lithium cages as well as a decrease of the intercage distance. Comparison to EIS shows that an increase in short-range movement translates into increased long-range movement in a straightforward manner for slow-cooled samples. However, for quench-cooled samples, this correlation is lost. Lattice softness and phonon-ion interactions are suggested to play an important role in long-range conduction which only becomes apparent when chemical composition and disorder are disentangled. This work shows that by altering one synthesis step, the relationship between site-occupancy-based descriptors (site disorder or S_conf) and lithium dynamics is changed profoundly. Furthermore, it shows that chemical composition and descriptors of site disorder cannot be seen as one and the same, as both play a role that changes with the length scale probed. Finally, it challenges the implicit assumption that increased short-range diffusivity automatically results in increased long-range diffusivity.

Phase separation, inducing a miscibility gap and non-monotonic open-circuit potential (OCP), is typical for widespread Li-ion battery electrodes such as LiFePO4, Li₄Ti₅OPhase separation, inducing a miscibility gap and non-monotonic open-circuit potential (OCP), is typical for widespread Li-ion battery electrodes such as LiFePO4, Li₄Ti₅O12 and Graphite. Although particle-scale effects of phase separation are well documented, its influence on transport-limited, porous electrodes remains largely overlooked. Here we embed physically consistent non-monotonic OCP profiles in a simplified Doyle–Fuller–Newman framework to compare their behavior against that of solid- solution materials with monotonic OCPs. Our findings provide deeper and general understanding of the different electrode ensemble behavior of solid solution (monotonic OCP) and phase separating (non-monotonic OCP) electrode materials, demonstrating why larger miscibility gaps are associated with decreasing rate capabilities and electrode utilization, amplifying local current heterogeneity and electrolyte depletion. By contrast, simulations employing conventional flat, fitted OCPs mask these effects and overpredict performance—particularly under dynamic cycling protocols such as galvanostatic intermittent titration (GITT). Our results reveal why accounting for realistic OCPs is essential for reliable modelling of high-loading electrodes, providing fundamental understanding and guidance for model-driven design and control of next-generation batteries and Graphite. Although particle-scale effects of phase separation are well documented, its influence on transport-limited, porous electrodes remains largely overlooked. Here we embed physically consistent non-monotonic OCP profiles in a simplified Doyle–Fuller–Newman framework to compare their behavior against that of solid- solution materials with monotonic OCPs. Our findings provide deeper and general understanding of the different electrode ensemble behavior of solid solution (monotonic OCP) and phase separating (non-monotonic OCP) electrode materials, demonstrating why larger miscibility gaps are associated with decreasing rate capabilities and electrode utilization, amplifying local current heterogeneity and electrolyte depletion. By contrast, simulations employing conventional flat, fitted OCPs mask these effects and overpredict performance—particularly under dynamic cycling protocols such as galvanostatic intermittent titration (GITT). Our results reveal why accounting for realistic OCPs is essential for reliable modelling of high-loading electrodes, providing fundamental understanding and guidance for model-driven design and control of next-generation batteries..

Anode-free aqueous zinc metal batteries (AZMBs) offer significant potential for energy storage due to their low cost and environmental benefits. Ti₃C₂T_x MXene provides several advantages over traditional metallic current collectors like Cu and Ti, including better Zn plating affinity, lightweight, and flexibility. However, self-freestanding MXene current collectors in AZMBs remain underexplored, likely due to challenges with Zn deposition reversibility. This study investigates the combination of a Ti₃C₂T_x self-freestanding film with advanced electrolyte engineering, specifically examining the effects of Li-salt and propylene carbonate (PC) as additives on Zn plating reversibility. While using Li⁺ ions as an additive alone facilitates uniform Zn deposition on bulk metals through the electrostatic shielding effect, the addition of Li-salt negatively impacts Zn plating uniformity on Ti₃C₂T_x. Meanwhile, using PC additive alone forms an organic SEI layer on Ti₃C₂T_x and causes Zn agglomeration. The use of both additives together results in a ZnF₂-containing hybrid SEI layer with improved interfacial kinetics, promoting more uniform Zn deposition. This approach achieves an average Coulombic efficiency (CE) of 96.8% over 150 cycles (a maximum CE of 97.8%). The study highlights the strategic difference in electrolyte design, emphasizing the need for tailored approaches to optimize Zn deposition on MXenes, contrasting with traditional metallic current collectors.

All-solid-state batteries receive ample attention due to their promising safety characteristics and energy density. The latter holds true if they are compatible with next-generation high-capacity anodes, but most highly ion-conductive solid electrolytes decompose at low operating potentials, leading to lithium loss and increased cell resistances. Here the dynamic stability of solid electrolytes that can improve all-solid-state battery performance is demonstrated. Halide electrolytes Li₃YCl₃Br₃ and Li₂ZrCl₆, considered unstable at low potentials, are found to exhibit structurally reversible redox activity beyond their electrochemical stability windows, increasing compatibility with anodes and contributing to capacity without compromising ionic conductivity. The benefit of this dynamic stability window is demonstrated with cost-effective red phosphorus anodes, resulting in high reversible capacities (2,308 mAh g⁻¹), high rate capacity retention (1,024 mAh g⁻¹ at 7.75 mA cm⁻²) and extended cycle life (61% retention after 1,780 cycles). Furthermore, high areal capacity (7.65 mAh cm⁻²) and stability (70% retention after 1,000 cycles) are achieved for halide-based full cells with red phosphorous anodes. The beneficial redox activity of halide electrolytes greatly expands their application scenarios and suggests valuable battery design principles to enhance performance.