Studies of Aluminum-Doped LiNi_0.5Co_0.2Mn_0.3O₂: Electrochemical Behavior, Aging, Structural Transformations, and Thermal Characteristics

Abstract

This paper is dedicated to studies of the electrochemical behavior, the structural and thermal features of the Ni-rich LiNi 0.5 Co 0.2 Mn 0.3 O 2 undoped and Al-doped (∼0.01 at.%) materials for positive electrodes of lithium batteries. We have found that structural characteristics of these materials are quite similar from the crystallographic point of view. It was demonstrated that Al substitution in the doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 is preferred at Ni sites over Co sites, and the thermodynamic preference for Al 3+ substitutions follows the order: Ni>Co>Mn. The lower capacity fading of the Al-doped electrodes upon cycling and aging of the cells in a charged state (4.3 V) at 60 • C, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The Al-doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes demonstrate also lower resistances of the surface film and charge-transfer as well as lower activation energies for the discharge process. From XPS studies we conclude that the modified stable and less resistive interface on the Al-doped particles comprises the Li + -ion conducting nano-sized centers like LiAlO 2 , AlF 3 , etc., which promote, to some extent, the Li + ionic transport to the bulk. A partial layered-to-spinel transformation was established upon cycling of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathodes.One of the major challenges in lithium batteries technology is, undoubtedly, the further improvement of battery components -electrodes, solutions, and separators. 1-7 Among several modern strategies to improve electrochemical performance and structural characteristics of materials for positive electrodes, doping has attracted the attention of scientists over the years. This is due to the effectiveness of dopants in stabilizing the structure of materials (even in minute amounts) and thus to increase the electrochemical cycling activity and to diminish the heat evolution of the electrodes in a charged state. A variety of dopant ions, like Co 2+ , Al 3+ , Ti 4+ , Zr 4+ , Zn 2+ , Fe 3+ , Cu 2+ , and Cr 3+ , has been used to improve the stability, morphology and microstructure of cathode materials, to enhance the electrode cycleability and rate capability, and to reduce capacity fading upon cycling. 8-13 For instance, doping of LiNi 0.5 Mn 0.5 O 2 with Co, Al, Ti resulted in decrease of the irreversible capacity loss and in almost no capacity fading of the doped electrodes. 14,15 In a systematic study of the Al-doped Ni-rich electrodes (LiNi 0.8 Co 0.15 Al 0.05 O 2 ), which are promising materials for use in batteries for electromotive applications, the authors have shown high cycling stability of these electrodes upon accelerated testing. 16 Several other doping metals, such as silver, magnesium, cobalt, gallium, lanthanum, bismuth, 17-19 as well as non-metallic ions (boron, fluorine), 20,21 were also explored in an attempt to increase the electrochemical cycling behavior of cathodes (both of layered and spinel structures) and to reduce their in...

Study of Cathode Materials for Lithium-Ion Batteries: Recent Progress and New Challenges

“…While small pores act as transport channels for ions to the bulk of the electrode, larger pores allow for easy mass transport of solvated ions [94,95]. [68,[96][97][98][99][100][101]. Dopants play various roles in the material.…”

“…The materials under examination were LiNi0.6Co0.2Mn0.2O2 and LiNi0.54Zr0.04Co0.2Mn0.2O2, synthesized by a [68,[96][97][98][99][100][101]. Dopants play various roles in the material.…”

“…On the one hand, they can act as pillars in the lithium layers and lead to the suppression of c-lattice contraction at the end of the charge, resulting in improved rate capability of the electrode [96]. Furthermore, with dopants occupying lithium sites, the Li + /Ni 2+ mixing can be reduced and, hence, the formation of inactive rock salt on the surface is suppressed, resulting in lower charge-transfer-resistance growth with cycling [96,97,102]. Since most of the synthetic strategies of NCM make use of the lithium excess to achieve the correct stoichiometry and minimize the cation mixing during annealing, the material has some excess lithium on the surface.…”

“…Nonetheless, it was shown that by adding 0.01 at % of Al-dopant to the material, the electrodes demonstrate lower capacity fading (Figure 16). Another study was dedicated to investigating the impact of minor aluminum doping (0.01 at %) of the NCM523 material prepared at BASF [97]. According to the synthetic procedure, Al doping took place at the expense of all the transition metals (Ni, Co, Mn).…”

Studies of the Electrochemical Behavior of LiNi0.80Co0.15Al0.05O2Electrodes Coated with LiAlO2

“…[3][4][5][6][7][8][9][10][11][12][13] In studies of LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333) cathodes, it was demonstrated 4-6 that they provided a capacity of 200 mAh/g in the voltage range of 2.5-4.6 V, or ∼155 mAh/g if the cutoff voltage is limited by 4.3 V.…”