磷酸锌改性提高正极材料LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)的电化学性能

Enhanced Electrochemical Performance of Zinc Phosphate Coated Ni-Rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) Cathode for Li-Ion Battery

富镍正极材料LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)具有低成本、可逆容量大等优势,是一种受到广泛研究的、极具商业化应用潜力的正极材料。然而高的镍含量会使电极表面结构不稳定性加剧,晶面间距降低,从而导致较差的循环性能与倍率性能。在采用共沉淀法制备纯样NCM811正极材料基础上,采用聚乙烯吡咯烷酮(PVP)辅助磷酸锌(Zn_(3)(PO_(4))_(2))包覆NCM811正极材料,XRD图谱表明,ZnO添加量(质量分数)3%时的改性样品(NCM2)的I_((003))/I_((104))值最大,c/a值较纯样的大,具有较低的Li^(+)/Ni^(2^(+))混排程度。同时,Zn^(2^(+))进入电极材料表面晶格,使晶面间距扩大,(003)平面内原子散射能力提升。X射线光电子能谱(XPS)、扫描电镜(SEM)及能谱(EDS)等表征结果表明,Zn_(3)(PO_(4))_(2)均匀包覆在正极材料颗粒表面。NCM2在0.1C电流密度下进行100次循环后的容量为191 mAh·g^(-1),容量保持率为92%,而未改性样品的容量保持率为87%。在5C电流密度下NCM2放电比容量比纯样高43%。循环伏安曲线和电化学阻抗谱结果表明,改性后正极材料电化学极化降低且Li^(+)扩散速率提高,提升了正极材料的循环性能和倍率性能。

Nickel-rich cathode material LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)has the advantages of low cost and large reversible capacity,so it has great potential for commercial application and becomes a hot spot for extensive research of new energy materials.However,high nickel content of Ni-rich cathode materials leads to increased surface structural instability and reduced interplanar spacing,as a result the cathode material shows poor cycle performance and rate performance in the commercial application.Based on the preparation of pure NCM811 by coprecipitation method,PVP(polyvinylpyrrolidone)assisted zinc phosphate coating NCM811 cathode material were synthesized.XRD patterns indicate that I_((003))/I_((104))of the coated sample with 3%ZnO addition(mass fraction,named NCM2)is the largest,and its c/a is bigger than that of the pristine,which means NCM2 has a lower degree of Li^(+)/Ni^(2^(+))mixing.At the same time,zinc ion insertion improves the atomic scattering ability in the(003)plane.X-ray photoelectron spectroscopy(XPS),scanning electron microscope(SEM),energy dispersive spectrometer(EDS)results show zinc phosphate is uniformly coated on the particle surface of cathode materials.The capacity of NCM2 after 100 cycles at the current density of 0.1C is 191 mAh·g^(-1),and the capacity retention rate is 92%,however,the capacity retention rate of the pure sample is 87%.At 5C current density,the discharge capacity of NCM2 is 43%higher than that of the pure sample.The cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)test results show that the electrochemical polarization of the cathode material decreases and the lithium ion diffusion rate increases after coating,As a result,the cycle performance and the rate performance of zinc phosphate coated NCM811 cathode material are improved.