Qidi Wang

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. The alternative text for this image may have been generated using AI.

Pairing high-energy nickel-rich cathodes with current collectors as anodes presents a compelling strategy to significantly boost the specific energy of rechargeable lithium-ion batteries, driving progress toward a transportation revolution. However, the limited active lithium inventory sourced by the cathodes tend to be rapidly consumed by irreversible Li plating/stripping and interfacial side reactions. To address these limitations, we propose a dual-gradient metal layer as an innovative solution to mitigate active Li loss by promoting uniform Li deposition and in situ formation of a stable solid electrolyte interphase. The operation of these batteries is investigated using a combination of electrochemical and chemical techniques to differentiate dead Li and interphase-bound Li inventory loss as well as material characterization methods to analyse the plated Li and interfacial composition and morphology. The developed dual gradient metal layer-based 600 mAh LiNi_0.9Co_0.05Mn_0.05O₂ | |Cu pouch cells achieve an areal capacity of 7.25 mAh cm^-2 and deliver an 80% capacity retention over 160 cycles. We show that the proposed approach is compatible with a range of different metal materials, offering a promising path toward next generation long-lasting, high-energy, initially active material-free anode based Li metal batteries.

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.

ConspectusLayered transition metal (TM) compounds are pivotal in the development of rechargeable battery technologies for efficient energy storage. The history of these materials dates back to the 1970s, when the concept of intercalation chemistry was introduced into the battery. This process involves the insertion of alkali-metal ions between the layers of a host material (e.g., TiS₂) without causing significant structural disruption. This breakthrough laid the foundation for Li-ion batteries, with materials like LiCoO₂ becoming key to their commercial success, thanks to their high energy density and good stability. However, despite these advantages, challenges remain in the broader application of these materials in batteries. Issues such as lattice strain, cation migration, and structural collapse result in rapid capacity degradation and a reduction in battery lifespan. Moreover, the performance of batteries is often constrained by the properties of the available materials, particularly in layered oxide materials. This has driven the exploration of materials with diverse compositions. The relationship between composition and structural chemistry is crucial for determining reversible capacity, redox activity, and phase transitions, yet predicting this remains a significant challenge, especially for complex compositions.In this Account, we outline our efforts to explore rational principles for optimal battery materials that offer a higher performance. The core of this is the concept of ionic potential, a parameter that measures the strength of the electrostatic interaction between ions. It is defined as the ratio of an ion's charge to its ionic radius, offering a quantitative way to evaluate interactions between cations and anions in crystal structures. By building on this concept, we introduce the cationic potential, which is emerging as a crystallographic tool that captures critical interactions within layered oxide materials. This approach provides insights into structural organization, enabling the prediction of P2- and O3-type stacking arrangements in layered oxides. A key advantage of using the cationic potential is its ability to guide the rational design of electrode materials with improved performance. For example, introducing P-type structural motifs into the material framework can significantly enhance ion mobility, mitigating detrimental phase transitions that often compromise battery efficiency and longevity. Furthermore, ionic potential serves as a representative parameter to quantitatively describe the properties of various TM compositions, providing a straightforward calculation method for designing multielement systems. We anticipate that this Account will provide fundamental insights and contribute to significant advancements in the design of layered materials, not only for battery applications but also for broader fields that require control of the material properties.

The kinetics of phase-separating electrodes (LFP, LTO, NVP) retain a rate-dependent memory effect, revealed by operando XRD and phase-field modelling, suggesting unconventional fast-charging protocols for improved battery management.

Electrode-electrolyte interphases are critical determinants of the reversibility and longevity of lithium (Li)-metal batteries (LMBs). However, upon cycling, the inherently delicate interphases, formed from electrolyte decomposition, become vulnerable to chemomechanical degradation and corrosion, resulting in rapid capacity loss and thus short battery life. Here, we present a comprehensive analysis of the complex interplay between the thermodynamic and kinetic properties of interphases on Li-metal anodes, providing insights into interphase design to address these challenges. Direct measurements of ion-transport kinetics across various electrolyte chemistries reveal that interphases with high Li-ion mobility are essential for achieving dense Li deposits. Conversely, sluggish ion transport generates high-surface-area Li deposits that induce Li random stripping and the accumulation of isolated Li deposits. Surprisingly, interphases that support long cycle life do not necessarily require the formation of dense Li deposits but must avoid possible electrochemical/chemical reactions between the Li-metal deposits and electrolytes' components. By that, in some specific electrolyte systems, isolated Li deposits can recover and electrically rejoin the active Li anodes' mass. These findings challenge conventional understanding and establish new principles for designing durable LMBs, demonstrating that even with commercial carbonate-based electrolytes, LiNi_0.8Co_0.1Mn_0.1O₂||Cu cells can achieve high reversibility.

The formation of stable interphases on the electrodes is crucial for rechargeable lithium (Li) batteries. However, next-generation high-energy batteries face challenges in controlling interphase formation due to the high reactivity and structural changes of electrodes, leading to reduced stability and slow ion transport, which accelerate battery degradation. Here, we report an approach to address these issues by introducing multicomponent grain-boundary-rich interphase that boosts the rapid transport of ions and enhances passivation toward prolonged lifespan. This is guided by fundamental principles of solid-state ionics and geological crystallization differentiation theory, achieved through improved solvation chemistry. Demonstrations showcase how the introduction of the interphase substantially impacts the Li-ion transport across the interphase and the electrode-electrolyte compatibility in cost-effective electrolyte solutions optimized with multiple Li salts. The resulting interphases feature microstructures rich in inorganic grain boundaries with a diverse array of nanosized grains, presenting enhanced Li-ion transport. Comprehensive analyses revealed that this realizes remarkable electrochemical stability over extended cycling periods by inhibiting electrode corrosion, thus holding promise for high-capacity thin-Li-metal, Si-based anodes, and even Li-free anodes when paired with high-capacity oxide cathodes. This work opens new avenues to customize protective interphases on high-capacity electrodes, promoting the development of batteries with the highest energy density using cost-effective electrolytes.

Effective optimization and control of lithium-ion batteries cannot neglect the relation between fundamental physicochemical phenomena and performance. In this work, we apply a multi-step charging protocol to commercially relevant electrodes, such as LiNi0.8Mn0.1Co0.1O2 (NMC811), LiFePO4 (LFP), LiMn1.5Ni0.5O4 (LMNO), LiMn0.4Fe0.6PO4 (LMFP), Li4Ti5O12 (LTO) and Na3V2(PO4)3 (NVP), to investigate how the initial rate affects their kinetic response. Remarkably, electrodes undergoing phase separation exhibit a pronounced counter-intuitive memory effect under high-rate operating conditions. Using operando micro-beam X-ray diffraction, the origin is demonstrated to be embedded in the rate-dependent multi-electrode particle dynamics. Developed phase-field electrochemical models capture the ensemble behavior of electrode particles underlying the kinetically induced memory effect, establishing how the thermodynamics of the nanoscale (particle) level affects macroscopic battery behavior under realistic conditions. These results challenge established battery management strategies, opening the doors for improved characterization and optimization of fast-charging protocols, crucial in minimizing aging and heat production while enhancing energy efficiency and benefitting a wide range of battery-powered applications.