钠离子电池P2-Na0.6Li0.27Mn0.73O2正极材料的W掺杂研究

Investigation of W-doped P2-Na0.6Li0.27Mn0.73O2 cathode materials for sodium-ion batteries

钠离子电池P2型层状氧化物可以通过掺杂一些非活性金属元素(Li、Mg)激发阴离子氧化还原反应以提升容量。然而,阴离子氧化还原反应具有固有的不可逆性和动力学迟滞的缺点。此外,在高电压下还存在晶格氧的不可逆损失和电解液的过度分解,导致电池容量的快速衰减和放电电位的持续降低。本文采用高温固相法合成了不同质量比W掺杂的P2型层状氧化物Na0.6Li0.27Mn0.73-xWxO2(NLMWO)。结合多种表征手段研究不同掺杂量的W元素对材料结构和电化学性能的影响。结果表明,W掺杂能够有效减少Na+/空位有序,抑制了P2-OP4-O2的相变,提高Na+的扩散速率。在2.0~4.6 V的电压范围内,0.5 C的倍率下,质量比1.0%W掺杂的改性材料Na0.6Li0.27Mn0.72W0.01O2(NLMWO-1)循环100次的容量保持率为80%;在5.0 C的倍率下,NLMWO-1的平均放电比容量为92.6 mAh/g,是Na0.6Li0.27Mn0.73O2(NLMO)的1.5倍。研究结果表明,非活性金属掺杂是抑制不可逆阴离子氧化还原的有效手段。该工作为高容量、高稳定性钠离子电池正极材料的结构设计提供了可行的思路。

Activating anion redox reactions in P2-type layered oxides is an effective strategy to achieve higher specific capacities for sodium-ion batteries.A common approach to realizing anion redox reactions involves substituting transition metals with elements such as lithium or magnesium.However,this strategy faces challenges due to the inherent irreversibility of the anion redox reaction and kinetic hysteresis.In addition,high-voltage conditions can lead to irreversible oxygen loss and excessive electrolyte decomposition,resulting in rapid capacity decay and a sustained decrease in discharge potential.In this study,W-doped P2-type layered oxide Na0.6Li0.27Mn0.73-xWxO2(NLMWO)was synthesized using a high-temperature solid-state method.The effects of varying W doping levels on the electrochemical performance of the materials were investigated through multiple characterization techniques.The results demonstrate that W doping effectively reduces Na+/vacancy ordering,suppresses the P2-OP4-O2 phase transition,and enhances Na+diffusion rates.The capacity retention of Na0.6Li0.27Mn0.72W0.01O2(NLMWO-1)with 1.0%W doping increased by 63.6%after 100 cycles at a rate of 0.5 C in the voltage range of 2.0—4.6 V,compared to Na0.6Li0.27Mn0.73O2(NLMO).At 5.0 C,NLMWO-1 delivers an average discharge specific capacity of 92.6 mAh/g,1.5 times that of NLMO,demonstrating excellent rate capability.These findings suggest that inactive metal doping can effectively mitigate the irreversible anion redox of transition metal layer oxides,providing valuable insights for the design of high-capacity and high-stability cathode materials for sodium-ion batteries.