高镍三元正极材料动力学性能的单颗粒研究
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摘要
镍钴锰三元材料LiNi_xCo_yMn_zO_2(x+y+z=1)在容量、倍率、循环及热稳定性等方面的性能往往受到金属元素Ni、Co、Mn含量的显著影响.其中,增加元素Ni的含量有助于提高材料的比容量.因此,LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2(NCM622)和LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2(NCM811)成为了目前研究最为广泛的两种高镍三元正极材料.但目前针对这两种材料的对比研究主要集中在材料比容量、热稳定性和循环稳定性的影响方面,而对材料动力学性能的研究较少,尤其是对材料本征动力学参数的表征尚未见报道.本文采用单颗粒微电极技术,以粒径相同的NCM622和NCM811颗粒为研究对象,排除导电剂、粘结剂和电极结构的影响,从材料本征动力学性能评估的角度出发,分析了Ni元素的含量对这两种材料的充放电性能、交流阻抗谱、锂离子固相扩散系数和倍率放电性能等的影响.结果表明,与NCM622相比,随着Ni~(2+)和Ni~(3+)总含量的增加,NCM811表现出更高的充放电容量、锂离子固相扩散系数、电化学反应活性和倍率放电性能.以20 C放电,NCM811材料的放电容量保持率仍可维持在80.8%以上.
Electrochemical performances such as capacity, rate, cycle and thermal stability of the nickel(Ni), cobalt(Co) and manganese(Mn) ternary cathode material, LiNi_xCo_yMnzO_2(x + y + z = 1), are significantly influenced by the proportion of Ni, Co,and Mn elements. To obtain higher specific capacity, LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2(NCM622) and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2(NCM811) with high amounts of Ni element were employed for the lithium ion batteries. By now, many studies have been focusing on the thermal and cycling stabilities of NCM622 and NCM811. However, there is lack of reports on the intrinsic kinetic properties of these two cathode materials. In this work, single particle microelectrode has been employed to investigate the intrinsic kinetic properties of NCM622 and NCM811 without the influences of binder, conductive agent, and electrode structure. Charge-discharge test, electrochemical impedance spectroscopy(EIS), and potentiostatic intermittent titration(PITT) methods were used for the evaluation of the kinetic properties of NCM622 and NCM811. Due to the increased Ni~(2+)/Ni~(3+) and decreased Mn~(4+)amounts, the NCM811 material presented better kinetics properties and higher columbic efficiency compared with NCM622. The discharge capacity retention of NCM811 was above 80.8% at 20 C compared to 0.5 C, which is much higher than that of NCM622 with 68.6%.
Electrochemical performances such as capacity, rate, cycle and thermal stability of the nickel(Ni), cobalt(Co) and manganese(Mn) ternary cathode material, LiNi_xCo_yMnzO_2(x + y + z = 1), are significantly influenced by the proportion of Ni, Co,and Mn elements. To obtain higher specific capacity, LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2(NCM622) and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2(NCM811) with high amounts of Ni element were employed for the lithium ion batteries. By now, many studies have been focusing on the thermal and cycling stabilities of NCM622 and NCM811. However, there is lack of reports on the intrinsic kinetic properties of these two cathode materials. In this work, single particle microelectrode has been employed to investigate the intrinsic kinetic properties of NCM622 and NCM811 without the influences of binder, conductive agent, and electrode structure. Charge-discharge test, electrochemical impedance spectroscopy(EIS), and potentiostatic intermittent titration(PITT) methods were used for the evaluation of the kinetic properties of NCM622 and NCM811. Due to the increased Ni~(2+)/Ni~(3+) and decreased Mn~(4+)amounts, the NCM811 material presented better kinetics properties and higher columbic efficiency compared with NCM622. The discharge capacity retention of NCM811 was above 80.8% at 20 C compared to 0.5 C, which is much higher than that of NCM622 with 68.6%.
引文
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[2]Bak S-M,Hu E Y,Zhou Y N,et al.Structural changes and thermal stability of charged Li NixMnyCozO2cathode materials studied by combined in situ time-resolved XRD and mass spectroscopy[J].ACS Applied Materials&Interfaces,2014,6(24):22594-22601.
[3]Noh H J,Youn S,Yoon C S,et al.Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2(x=1/3,0.5,0.6,0.7,0.8 and 0.85)cathode material for lithium-ion batteries[J].Journal of Power Sources,2013,233:121-130.
[4]Wei Y,Zheng J X,Cui S H,et al.Kinetics tuning of Li-ion diffusion in layered Li(NixMnyCoz)O2[J].Journal of the American Chemical Society,2015,137(26):8364-8367.
[5]Uchida I,Fujiyoshi H,Waki S,et al.Microvoltammetric studies on single particles of battery active materials[J].Journal of Power Sources,1997,68(1):139-144.
[6]Dokko K,Nishizawa M,Horikoshi S,et al.In situ observation of Li Ni O2single-particle fracture during Li-ion extraction and insertion[J].Electrochemical and Solid-State Letters,2000,3(3):125-127.
[7]Munakata H,Takemura B,Saito T,et al.Evaluation of real performance of Li Fe PO4by using single particle technique[J].Journal of Power Sources,2012,217:444-448.
[8]Huang Y H,Wang F M,Huang T T,et al.Micro-electrode linked cyclic voltammetry study reveals ultra-fast discharge and high ionic transfer behavior of Li Fe PO4[J].International Journal of Electrochemical Science,2012,7(2):1205-1213.
[9]Dokko K,Nakata N,Suzuki Y,et al.High-rate lithium deintercalation from lithiated graphite single-particle electrode[J].The Journal of Physical Chemistry C,2010,114(18):8646-8650.
[10]Zuleta M,Bjornbom P,Lundblad A.Effects of pore surface oxidation on electrochemical and mass-transport properties of nanoporous carbon[J].Journal of The Electrochemical Society,2005,152(2):A270-A276.
[11]Nishikawa K,Munakata H,Kanamura K.In-situ observation of one silicon particle during the first charging[J].Journal of Power Sources,2013,243:630-634.
[12]Nishikawa K,Moon J,Kanamura K.In-situ observation of volume expansion behavior of a silicon particle in various electrolyte[J].Journal of Power Sources,2016,302:46-52.
[13]Wang F Q(王福庆),Wei Y M(魏奕民),Su Y Z(苏育专),et al.Fast and accurate evaluation of Li Fe PO4cathode materials by single particle microelectrode[J].Journal of Electrochemistry(电化学),2015,21(6):566-571.
[14]Miller D J,Proff C,Wen J G,et al.Observation of microstructural evolution in Li battery cathode oxide particles by In situ electron microscopy[J].Advanced Energy Materials,2013,3(8):1098-1103.
[15]Xie J,Imanishi N,Zhang T,et al.Li-ion diffusion kinetics in Li Fe PO4thin film prepared by radio frequency magnetron sputtering[J].Electrochimica Acta,2009,54(20):4631-4637.