Key Takeaways & Executive Findings
- •• • W doping refines primary particle size and stacking, increasing average particle hardness from 68 MPa (PCNCM98) to 104 MPa (W-PCNCM98), a 1.5-fold improvement that suppresses microcrack formation during H2–H3 phase transition, directly addressing mechanical degradation in ultrahigh-nickel cathodes. • • W-PCNCM98 achieves 73% capacity retention after 2000 cycles at 1 C and 25 °C in pouch full cells, a 54% relative improvement over PCNCM98, demonstrating enhanced cycling stability critical for EV longevity. • • Thermal stability is improved: exothermic peak shifts from 190 °C (PCNCM98) to 203 °C (W-PCNCM98), with heat generation reduced from 1528 J g−1 to 1287 J g−1, mitigating safety risks from oxygen release. • • W6+ doping suppresses transition metal dissolution and reduces leak current density in floating charge tests, indicating robust electrode–electrolyte interfacial stability, which is essential for long-term reliability.
Abstract
Utilization of ultrahigh-nickel LiNi_xCo_yMn_1-x-yO_2 (NCM) (x > 0.97) in Li-ion batteries can distinctively boost energy density through enhanced discharge capacity. However, capacity and thermal stability deteriorate as Ni content approaches the limit. Here, we propose a facile strategy by introducing high-valence tungsten (W) into ultrahigh-nickel polycrystalline LiNi_0.98Co_0.01Mn_0.01O_2 (PCNCM98). W-doped PCNCM98 (W-PCNCM98) exhibits refined, compactly stacked primary particles, whereas PCNCM98 shows equiaxial, non-uniform larger particles. The refined microstructure enhances mechanical strength: average particle hardness of W-PCNCM98 is 104 MPa, 1.5 times higher than PCNCM98 (68 MPa). This improved mechanical property suppresses lattice volume changes and relieves microcrack formation from H2–H3 phase transition. Consequently, cycling performance in pouch-type full cells is significantly enhanced, with capacity retention of 73% after 2000 cycles at 1 C and 25 °C, 54% higher than PCNCM98. Enhanced structural stability and strong electron affinity of W6+ also improve thermal stability: exothermic peak for W-PCNCM98 is postponed to 203 °C with heat generation of 1287 J g−1, versus 190 °C and 1528 J g−1 for PCNCM98. This high-valent doping strategy stabilizes ultrahigh-nickel NCM cathodes, accelerating large-scale EV applications.
1. Introduction
Ultrahigh-nickel layered oxide cathodes (Ni ≥ 0.97) promise higher energy density for electric vehicles, yet their commercial deployment is stalled by severe capacity fading and thermal instability. The root cause lies in the mechanical fragility of primary particles, which undergo anisotropic lattice volume changes during the H2–H3 phase transition at high state of charge, leading to intergranular microcracks and subsequent electrolyte attack. Previous attempts to mitigate this via elemental doping or surface coating have achieved limited success, often sacrificing capacity or adding process complexity.
This work introduces a high-valence tungsten doping strategy that simultaneously refines primary particle morphology and enhances mechanical stiffness. By increasing particle hardness from 68 MPa to 104 MPa, the W-doped cathode effectively accommodates internal stress, suppressing microcrack formation. This structural reinforcement translates into a 54% improvement in capacity retention over 2000 cycles and a delayed exothermic peak by 13 °C, addressing both cycling and safety bottlenecks. The approach offers a scalable pathway to stabilize ultrahigh-nickel cathodes without compromising energy density.
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Xiaozhen Zhang, Shanshan Bi, Jiande Lin, Yang Ding, Lufeng Yang, Junye Yang, Jianming Zheng, Ying Lin, Xunxin Chen, Zhifeng He, Haitang Zhang, Ang Fu, Yixiao Li, Yong Cheng, Mingzeng Luo, Chuanjing Xu, Yaxin Huang, Deyin Wu, Pengfei Yan, Yu Qiao, Ming-Sheng Wang, Kazumasa Takeshi, Yuli Li, Haipeng Guo, Yan Zhou, Li Wang, Jie Chen, Yong Yang (2026). Promoting cycling and thermal stability of ultrahigh-nickel oxide cathodes with well-controlled microstructure and stiffness. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4079-4
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Frequently Asked Questions
What is the specific mechanism by which tungsten doping enhances the mechanical strength of the cathode, and how does this translate to improved cycling performance?
Tungsten doping refines primary particle size and promotes compact stacking, increasing particle hardness from 68 MPa to 104 MPa. This enhanced stiffness suppresses lattice volume changes during H2–H3 phase transition, preventing microcrack formation. Consequently, capacity retention improves to 73% after 2000 cycles at 1 C, a 54% relative increase over undoped PCNCM98.
How does tungsten doping affect the thermal stability of the ultrahigh-nickel cathode, and what are the safety implications?
W6+ has strong electron-withdrawing capability, which suppresses oxygen release from the lattice. This shifts the exothermic peak from 190 °C to 203 °C and reduces heat generation from 1528 J g−1 to 1287 J g−1, lowering the risk of thermal runaway in battery packs.
What is the impact of tungsten doping on the interfacial stability between the cathode and electrolyte?
W doping reduces transition metal dissolution and lowers leak current density in floating charge tests, indicating a more robust electrode–electrolyte interface. This improves cycling stability and reduces parasitic reactions, contributing to longer battery life.
What are the scalability and cost implications of the tungsten doping strategy for commercial production?
The doping method is described as facile and effective, likely involving standard solid-state synthesis with tungsten precursors. While specific cost data are not provided, the use of tungsten in small amounts (likely <1 mol%) and the significant performance gains suggest a favorable cost-performance trade-off for large-scale EV applications.
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