The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the reme...The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.展开更多
近年来,锂离子电池因其能量密度大,循环性能优越,无记忆效应及绿色环保无污染等特点,符合社会发展的需求,被广泛应用于消费类移动电子产品、电动工具、航空航天、医疗设备、电动汽车电源及储能等各个领域。而正极材料是决定锂离子电池...近年来,锂离子电池因其能量密度大,循环性能优越,无记忆效应及绿色环保无污染等特点,符合社会发展的需求,被广泛应用于消费类移动电子产品、电动工具、航空航天、医疗设备、电动汽车电源及储能等各个领域。而正极材料是决定锂离子电池性能和成本的关键因素,因此高性能正极材料的开发和改性成为锂离子电池领域的研究热点。在Li Co O_(2),Li Mn O_(2),Li Fe PO_(4)等众多正极材料中,三元正极材料Li Ni_(x)CoyMn_(1-x-y)O_(2),尤其是高镍三元材料(x≥0.6)因其放电比容量高、成本低廉及环境友好等优点,成为动力电池首选材料之一,但材料突出的循环性能、安全性能和倍率性能较差等问题在很大程度上阻碍了其规模化应用。介绍了高镍三元材料自身固有的缺陷和充放电过程中产生的一系列继发劣变,如表界面不稳定、Li^(+)/Ni^(2+)混排,不可逆相转变、微裂纹、有效组分溶解等,综述了近期对高镍三元材料进行的体相掺杂、表面包覆、单晶化、梯度结构方面的改性研究及相关成果,并对高镍三元材料改性方案进行了分析和展望。展开更多
基金the support from the Natural Science Foundation of China(No.51871118)Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education,Lanzhou University,China(No.LZUMMM2021005)+1 种基金the Science and Technology Project of Lanzhou City,China(No.2019-1-30)State Key Laboratory of Special Rare Metal Materials,China(No.SKL2020K003)。
文摘The hexagonal to orthorhombic(HO)transformation fromβ-Ni_(3)Sn_(2)(hexagonal)phase toα'-Ni_(3)Sn_(2)(orthorhombic)phase was confirmed in directionally solidified Sn−Ni peritectic alloys.It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting(TGZM)and Gibbs−Thomson(G−T)effects can take place on secondary dendrites.Besides,the intersection angle between the primary dendrite stem and secondary branch(θ)is found to increase fromπ/3 toπ/2 as the solidification proceeds.This is the morphological feature of the HO transformation,which can change the diffusion distance of the remelting/resolidification process.Thus,a diffusion-based analytical model is established to describe this process through the specific surface area(S_(V))of dendrites.The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification.In addition,the slope of the prediction curves is changed,indicating the variation of the local remelting/resolidification rates.
文摘近年来,锂离子电池因其能量密度大,循环性能优越,无记忆效应及绿色环保无污染等特点,符合社会发展的需求,被广泛应用于消费类移动电子产品、电动工具、航空航天、医疗设备、电动汽车电源及储能等各个领域。而正极材料是决定锂离子电池性能和成本的关键因素,因此高性能正极材料的开发和改性成为锂离子电池领域的研究热点。在Li Co O_(2),Li Mn O_(2),Li Fe PO_(4)等众多正极材料中,三元正极材料Li Ni_(x)CoyMn_(1-x-y)O_(2),尤其是高镍三元材料(x≥0.6)因其放电比容量高、成本低廉及环境友好等优点,成为动力电池首选材料之一,但材料突出的循环性能、安全性能和倍率性能较差等问题在很大程度上阻碍了其规模化应用。介绍了高镍三元材料自身固有的缺陷和充放电过程中产生的一系列继发劣变,如表界面不稳定、Li^(+)/Ni^(2+)混排,不可逆相转变、微裂纹、有效组分溶解等,综述了近期对高镍三元材料进行的体相掺杂、表面包覆、单晶化、梯度结构方面的改性研究及相关成果,并对高镍三元材料改性方案进行了分析和展望。
