Synthesis of Single Crystal LiNi_0.5Mn_0.3Co_0.2O₂for Lithium Ion Batteries

Abstract

Single crystal Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 materials in NMC532/artificial graphite cells have excellent long term charge-discharge cycle lifetime which greatly exceeds that of conventional NMC532 materials. There are a few patents from industry regarding the synthesis of single crystal NMC. In addition, there have only been a few reports in the academic literature showing that single crystal NMC with a grain size of ∼2-5 μm having good electrochemical performance was successfully synthesized, but these workers used complex approaches. This work systematically studies the steps required to synthesize single crystal NMC materials. The key synthesis steps including the impact of the Li to transition metal ratio, sintering temperature, precursor size and sintering time are discussed. This work provides guidance for the synthesis of single crystal NMC positive electrode materials that may be suitable for lithium-ion cells with high energy density and long lifetime. 1, the authors briefly discussed the synthesis method for single crystal materials, while the detailed information regarding the impact of the steps required to synthesize single crystal NMC materials was not discussed. In this work, the key synthesis steps including the impact of lithium to transition metal (Li/TM) ratio (molar), sintering temperature, sintering time and precursor size will be discussed. The optimization of the final synthesis conditions and evaluation of the electrochemical stability of the materials is not the main focus of this paper. However, the initial electrochemical properties, such as reversible specific capacity and irreversible specific capacity, of the best materials in this report are certainly competitive to commercial NMC532 materials. ExperimentalReagents used for the synthesis of single crystal NMC532 included nickel (II) sulfate hexahydrate (NiSO 4 • 6H 2 O, 98%, Alfa Aesar), manganese sulfate monohydrate (MnSO 4 • H 2 O, 98%, Alfa Aesar), sodium hydroxide (NaOH, 98%, Alfa Aesar), ammonium hydroxide (NH 4 OH, 28.0-30.0%, Sigma-Aldrich). All aqueous solutions used in the precursor synthesis were prepared with deionized (DI) water which was de-aerated by boiling for 10 minutes. Reagents used for coin cells included 1:2 v/v ethylene carbonate:diethyl carbonate (EC:DEC, BASF, purity 99.99%) and lithium hexafluorophosphate (LiPF 6 , BASF, purity 99.9%, water content 14 ppm).Synthesis of single crystal NMC532.-Ni 0.5 Mn 0.3 Co 0.2 (OH) 2 precursors were prepared via co-precipitation in a continuously stirred tank reactor (CSTR) (Brunswick Scientific/Eppendorf BioFlo 310). 9The details of the synthesis of similar precursors has been described by J. Li et al. 10,11 Precursors with three different sizes, labelled as large (L), medium (M) and small (S), were prepared individually by adjusting the pH and stirring rate. Unless specified, precursor L was * Electrochemical Society Fellow.z E-mail: jeff.dahn@dal.ca used for the synthesis of lithiated samples. The dried precursors were mixed with a stoichiometric equivalent of Li 2 CO ...

Synthesis of Single Crystal LiNi0.6Mn0.2Co0.2O2with Enhanced Electrochemical Performance for Lithium Ion Batteries

“…Consistent with the work shown by J. Li et al, 7 Figure 5a shows that at a fixed sintering temperature, an increase in excess lithium results in a decrease in capacity because there is less available transition metal redox capacity in Li 1+x NMC (1−x) O 2 when x increases (more Ni 3+ and less Ni 2+ ions). Figure 5a shows that samples synthesized at 940…”

“…Figure 1 shows that with a fixed Li/TM ratio, an increase in sintering temperature assists with particle growth, even though high temperature sintering leads to more lithium loss. Compared to the reported SC532 synthesis, 7 which requires a sintering temperature of 970…”

“…For example, Arumugam et al 2 showed that an Al 2 4 T. Kimijima et al 5 showed that single crystal NMC111 could be synthesized using a molten salt method, and a similar method was also applied by Y. Kim et al 6 to synthesize single crystal NMC811. J. Li et al 7 introduced a method to synthesize single crystal NMC532 and explored the impact of key synthesis parameters. It was found that the lithium/transition metal molar ratio and sintering temperature played important roles in the synthesis.…”

“…14 In this study, large sized precursor 1 ( Figure 1A) was used to make conventional polycrystalline NMC622 (PC622) because conventional PC622 generally have particles in the size of 10-15 μm. Precursor 2 ( Figure 1B) was used for single crystal NMC622 (SC622) synthesis because according to the previous work by Li et al, 7 smaller sized precursors can alleviate primary particle agglomeration after sintering. The morphology differences between precursor 1 and precursor 2 originate from the difference in pH during synthesis.…”

Surface and Interfacial Chemistry in the Nickel‐Rich Cathode Materials

“…To mitigate the cathode reactivity with the electrolyte, there are five approaches for the development of high energy LIBs: (1) the incorporation of electrochemically inactive elements into the cathode structure, [30][31][32][33][34][35][36][37] (2) the introduction of the concentration gradient, (3) the introduction of surface coating layer on the cathode, [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] (4) the morphological changes to the porous structure, and (5) the crystallinity tuning from the polycrystalline to the single crystalline cathode. [57][58][59][60][61][62][63][64][65][66] With respect to the first approach, it could improve the interfacial stability by inhibiting the transition metal reductions. Furthermore, the nickel-rich cathodes with the concentration gradient could also enhance the interfacial stability by mitigating the micro-crack formations during the electrochemical test.…”