On April 16, researchers Liu Zhaoping and Qiu Bao, along with their team from the Power Lithium Battery Engineering Laboratory at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, published a groundbreaking study titled “Negative-thermal expansion and oxygen-redox electrochemistry” in the prestigious scientific journal Nature.
The team discovered an unusual phenomenon in high-capacity lithium-rich manganese-based cathode materials, where they exhibited lattice shrinkage when exposed to heat. This “heat-induced shrinkage” could potentially help restore voltage in aging lithium batteries, effectively rejuvenating them. This discovery offers a novel approach to developing smarter and more durable next-generation high-energy lithium batteries, which could revolutionize battery design and usage in the future.
To enhance the range of electric vehicles and electric aircraft, the development of high-energy lithium batteries is crucial. Lithium-rich manganese-based cathode materials are considered ideal candidates for the next generation of lithium battery cathodes due to their high discharge capacity of up to 300mAh/g, thanks to additional oxygen redox capacity. This capacity is significantly higher than that of current cathode materials, offering the potential to increase energy density by over 30%, with substantial cost advantages.
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However, these materials face issues with voltage decay in practical applications, which affects their long-term stability. The root cause of this problem lies in the asymmetry of oxygen activity during charge and discharge cycles, leading to high energy input during charging and low energy release during discharge. This imbalance causes continuous energy accumulation in the lattice, which drives irreversible structural changes. The instability of the dynamic balance between oxygen activity and lattice stability triggers structural damage, leading to voltage drop and capacity degradation. Therefore, achieving long-term stability in high-energy lithium batteries remains a critical challenge for next-generation battery technology.
Using in-situ heated synchrotron X-ray diffraction (SXRD) characterization, the research team was the first to capture the anomalous shrinkage behavior of lithium-rich manganese-based cathode materials at high temperatures. They confirmed that this phenomenon is also present in other oxygen-active cathode materials, defying the conventional “thermal expansion” principle followed by most solid materials. Specifically, between temperatures of 150°C and 250°C, the cell volume of these cathode materials not only failed to expand but also showed an unusual negative thermal expansion (NTE) effect.
This finding challenges the classical theory of thermal expansion and reveals a unique mechanism by which structural disorder governs the material’s thermodynamic behavior. It opens up new possibilities for the design of novel functional materials, linking structural disorder directly with lattice thermodynamics. This could provide new insights into the complex energy storage mechanisms in oxygen-active cathode materials.
To understand the physical and chemical nature of the NTE effect, the team combined charge-discharge testing with thermodynamic calculations. They discovered a reversible transition mechanism of structural disorder in the oxygen framework: under heating, the disordered structure in metastable materials shifts toward dynamic ordering, which leads to the anomalous shrinkage of the lattice parameters. Based on this, the team established a quantitative relationship between the reversible oxygen capacity contribution (γ) and the negative thermal expansion coefficient (α): α = -0.463γ + 14.4×10^-6 °C^-1. By controlling the oxygen activity contribution through chemical composition adjustments, the team successfully developed new materials with a thermal expansion coefficient close to zero, achieving a significant leap from observational discovery to quantitative design.
This research has made two major methodological breakthroughs:
- It developed a dynamic characterization technique for the degree of structural disorder based on thermally activated kinetics, overcoming the limitations of traditional static structural analysis for metastable systems.
- It introduced a “structural disorder-functionality” reverse design strategy, optimizing material thermal expansion behavior through controlled oxygen activity.
This design concept of regulating disorder into order not only provides a new pathway for developing zero thermal expansion electrode materials but also pioneers a new research paradigm in functional materials based on dynamic structural evolution.
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Additionally, the research team established an “electrochemical annealing” model based on nonequilibrium thermodynamics, achieving dynamic control of metastable materials in electrochemical systems for the first time.
Key experimental evidence showed that at a critical voltage of 4.0 V, the lithium-rich manganese-based cathode material exhibited a unique voltage memory effect. Its lattice oxygen reconstruction activation energy was significantly reduced, driving structural disorder to reorganize into an ordered state, achieving nearly 100% voltage recovery.
These discoveries present a promising new strategy for extending the lifespan of lithium-rich manganese-based batteries. By intelligently adjusting charging strategies, structural issues in the cathode material can be periodically repaired, significantly prolonging battery life. This study not only deepens our understanding of material thermodynamics but also provides essential theoretical guidance for the design of new functional materials and optimization of battery performance.