A new dopant-pairing strategy can boost the stability of cathodes for lithium-ion batteries

Lithium-ion batteries (LiBs), rechargeable batteries that move lithium ions between the anode (i.e., negative electrode) and cathode (i.e., positive electrode), are used to power most portable electronics on the market today. These batteries have various advantageous properties, including a relatively long lifespan, light weight and good energy density in proportion to their size.

Over the past decades, energy engineers have been trying to devise strategies to further increase these batteries’ energy density and durability over time. This could contribute to the future advancement of various types of electronics, including smartphones, laptops, wearable devices and electric transportation vehicles.

One approach to increase the energy density of batteries entails the design or enhancement of cathode materials, the electrode in battery cells that attracts positive ions. Past studies showed that layered cathode materials with a high nickel content can increase the maximum charging voltage of LiBs. Nonetheless, their use also typically reduces a battery’s cycling stability, prompting it to degrade faster over repeated charging-discharging cycles.

Researchers at Peking University, Shanghai Jiao Tong University, the Chinese Academy of Sciences and other institutes recently devised a promising strategy to stabilize layered cathodes, which could in turn improve the durability of high-energy LiBs, slowing their degradation time. Their approach, outlined in a paper published in Nature Energy, entails the addition of dopants (i.e., foreign atoms) to the Ni-rich materials.

“High-energy-density lithium-ion batteries for extreme conditions require cathodes that remain stable under harsh operation, including ultrahigh cutoff voltage and extreme temperatures,” wrote Hengyi Liao, Yufeng Tang, and their colleagues in their paper.

“For Ni-rich layered cathodes, raising the charge voltage from 4.3 V to 4.8 V (versus Li⁺/Li) increases the energy density, yet this sacrifices cycling stability and remains challenging. We report a dopant-pairing method that achieves highly enriched Ti⁴⁺ (~9-nm surface layer) in LiNi_0.8Co_0.1Mn_0.1O₂ facilitated by Na⁺, enabling significantly enhanced high-voltage cyclability. Such high surface Ti⁴⁺ concentrations are unattainable without pairing Na⁺, representing a form of supersaturation within the layered cathode matrix.”

Essentially, the researchers proposed pairing titanium ions (Ti⁴⁺) with sodium ions (Na⁺) to produce a thin and Ti⁴⁺-rich surface layer on an Ni-rich cathode. The high concentration of Ti⁴⁺ on the surface of the cathode material was found to enhance the material’s structural integrity, limiting undesirable side reactions that can prompt its degradation.

“The enhanced stability is linked to improved structural integrity and reduced cathode–electrolyte side reactions (for example, O₂ and CO₂ evolution),” wrote the authors. “In addition, ion transport is better preserved even after prolonged cycling at 4.8 V. This work highlights the power of supersaturated high-valence d⁰ cation M^z+ (z ≥ 4) in modifying the cathode–electrolyte interactions and degradation pathway.”

This recent study introduces a new viable path for creating LiBs that are both high-energy and durable. Other research teams could soon adapt the strategy devised by these researchers and test the performance of LiBs integrating the resulting cathode materials. In the future, the new dopant pairing-based approach could contribute to the development of next-generation LiBs for demanding real-world applications, such as electric vehicles and grid-scale energy storage.

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