Chen Shuyuan, Cheng Chen, Xia Xiao, Wang Lei, Chen Tong, Shen Yihao, Zhou Xi, Xv Weidong, Zhou Zheng, Zeng Pan, Zhang Liang
Institute of Functional Nano & Soft Materials (FUNSOM), Suzhou, Jiangsu, 215123, China.
Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, Suzhou, Jiangsu, 215123, China.
Small. 2024 Dec;20(50):e2406542. doi: 10.1002/smll.202406542. Epub 2024 Sep 23.
P2-type Mn-based layered oxides have emerged as one of the most promising cathode materials for sodium-ion batteries owing to their advantages of facile preparation and high theoretical capacity. However, challenges such as phase transition and irreversible oxygen release during cycling often lead to rapid structural distortion and the formation of oxygen vacancies, ultimately resulting in rapid capacity decay. Herein, a covalency modulation strategy is adopted to address these challenges and successfully achieved a stable P2-type Mn-based layered oxide by introducing strong covalent Ni─O bonds. The robust Ni─O motif plays a crucial role in maintaining the rigidity of transition metal (TM) layered frameworks, which efficiently alleviates the structural distortion and degradation of the coordination environments of local TM sites, thereby achieving durable structural stiffness over extended cycles. In addition, the strong covalent Ni─O bonds can also stabilize the local oxygen environment, effectively suppressing the irreversible oxygen release. Benefiting from these advancements, the as-designed NaMgMnNiO cathode displays a full solid-solution behavior with a low volume change of only 0.9% and an enhanced reversibility of lattice oxygen redox (OR) reaction. This investigation emphasizes the crucial role of covalency modulation in regulating OR chemistry and structural integrity to achieve high-energy-density Mn-based layered oxides.
P2型锰基层状氧化物因其制备简便和理论容量高的优点，已成为钠离子电池最有前景的正极材料之一。然而，诸如循环过程中的相变和不可逆氧释放等挑战，常常导致快速的结构畸变和氧空位的形成，最终导致容量快速衰减。在此，采用共价性调制策略来应对这些挑战，并通过引入强共价Ni─O键成功制备出稳定的P2型锰基层状氧化物。坚固的Ni─O motif在维持过渡金属（TM）层状框架的刚性方面起着关键作用，有效缓解了局部TM位点配位环境的结构畸变和降解，从而在长时间循环中实现持久的结构刚度。此外，强共价Ni─O键还能稳定局部氧环境，有效抑制不可逆氧释放。受益于这些进展，所设计的NaMgMnNiO正极表现出全固溶体行为，体积变化仅为0.9%，且晶格氧氧化还原（OR）反应的可逆性增强。本研究强调了共价性调制在调节OR化学和结构完整性以实现高能量密度锰基层状氧化物方面的关键作用。
