高镍正极材料中钴元素的替代方案及其合成工艺优化

An Optimized Synthetic Process for the Substitution of Cobalt in Nickel-Rich Cathode Materials

高镍三元正极材料LiNi_(x)Mn_(y)Co_(1−x−y)O_(2)(x>0.8)因其高能量密度而备受瞩目。在高镍三元正极材料中,Co不但有助于增强层状正极材料结构稳定性,而且能够提高正极材料导电性能,因此被认为是一种非常重要的元素。但是由于目前全球范围内钴矿资源紧缺,在一定程度上限制了含钴正极材料在新能源电动汽车领域的发展应用。基于此,本文将不同的过渡金属离子掺杂到高镍层状材料中形成无钴化正极材料,并进行高镍正极材料无钴化的可行性分析。通过实验对比发现,资源存储量丰富并且价格低廉的Zr在一定程度上可以取代Co元素,得到的正极材料LiNi_(0.85)Mn_(0.1)Zr_(0.05)O_(2)表现出良好的电化学性能,在0.2C倍率以及2.75–4.3 V的截止电压范围内,其放电比容量为179.9 mAh·g^(−1),80周容量保持率为96.52%。

High-performance rechargeable lithium ion batteries have been widely applied in electrochemical energy storage fields,such as,energy storage grids,portable electronic devices,and electric vehicles(EVs).However,the energy density of lithium ion batteries needs to be increased,and the cost of battery materials could be further reduced for wider commercial applications.An Ni-rich cathode,LiNi_(x)Mn_(y)Co_(1−x−y)O_(2)(x>0.8),with high specific capacity is the most promising material for next-generation Li-ion batteries.LiNi_(x)MnyCo_(1−x−y)O_(2)(x>0.8)contains three transition metal elements,Ni,Mn,and Co,respectively.The role of Ni2+is to provide high capacity for recharge The role of Mn4+is to stabilize the lattice structure during charging-discharging cycling.Crucially,the role of Co^(3+)in Ni-rich materials is to improve the electrical conductivity and inhibit cation disorder in the lattice during electrochemical cycling.However,Co is both in shortage and expensive,which limits its worldwide commercial application.This work investigates substituting Co with other abundant and cheap transition metals.Transition metal ions Cr3+,Cd2+,and Zr^(4+)can replace Co^(3+)in Ni-rich cathode materials.LiNi0.8Cr0.1Mn0.1O2,LiNi0.8Cd0.1Mn0.1O2,and LiNi_(0.8)Zr_(0.1)Mn_(0.1)O_(2) were synthesized by a co-precipitation method.Zr was found to be the best candidate for replacing Co in Ni-rich cathode materials.This study investigated Zr^(4+)-doped Co-free Ni-rich materials.Initially,a carbonate co-precipitation process was used to synthesize Ni_(0.8)Zr_(0.1)Mn_(0.1)CO_(3).This is due to that Zr3+/Zr^(4+)ions are not precipitated in the strong alkali solution,and the pH during hydroxide co-precipitation and carbonate co-precipitation processes are approximately 11 and 8,respectively.Therefore,the carbonate co-precipitation synthesis method was chosen.Ni_(0.8)Zr_(0.1)Mn_(0.1)CO_(3) was synthesized by carbonate co-precipitation at pH=7.6,7.8,8.0,and 8.2.After electrochemical analysis,pH=7.8 was identified as the optimal value.The next stage of the research involved completing an electrochemical performance comparison on two lithium sources.The following lithium sources were added to the precursor;LiOH·H2O,and a 1:1 mixture of LiOH·H2O and Li2CO3.The lithium source with the 1:1 mixture,exhibited better performance for the Ni-rich cathode,LiNi_(0.8)Zr_(0.1)Mn_(0.1)O_(2).In this study,the ideal doping amount of Zr in Ni-rich materials was 0.05.In conclusion,by careful control of co-precipitation pH and Li source,the Zr doped cobalt free Ni-rich cathode LiNi_(0.85)Mn_(0.1)Zr_(0.05)O_(2) delivered a discharge capacity of 179.9 mAh·g^(−1) at 0.2C.This was achieved between the voltage range of 2.75–4.3 V,with an 80 cycle capacity retention of 96.52%.