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Aqueous Processing of LiNi0.5Mn0.3Co0.2O2 Composite Cathodes for Lithium-Ion Batteries
Recently, there has been growing interest in switching fabrication of composite electrodes for lithium-ion batteries (LIBs) to aqueous systems due to advantages in low cost and environmental effect 1. Aqueous processing for conventional graphite anode is relatively mature, but remains challenging for the diverse array of LIB cathodes. Some success has been achieved on LiFePO4 2-4, LiCoO25, LiNi1/3Mn1/3Co1/3O2 (NMC333) 6, lithium-and manganese-rich NMC 7. In this work, NMC532 cathodes were fabricated through aqueous processing with different water soluble binder and dried at various conditions. The effect of binders and residual moisture on the electrode performance was evaluated.
Experimental
NMC532 aqueous suspension was mixed with a planetary mixer and coated by a slot-die coater. The cathode consiss of 90wt% NMC532, 5 wt% Denka carbon black, 4 wt% water soluble binder, and 1 wt% carboxymethyl cellulose (CMC) as dispersant/binder. Four binders were investigated. Al current collected was treated by corona plasma for improved wettability of the aqueous suspension 8.The electrodes were also dried at various temperatures resulting in different residual moisture in the electrodes when being assembled into coin cells. Electrode performance was evaluated in both half and full coin cells. Half cells were assembled with NMC532 and Li metal as the cathodes and anodes, respectively. A12 graphite anode was selected as the anode in full cells. A Celgard 2325 separator was placed between the cathode and anode. The electrolyte was 1.2 M LiPF6in ethylene carbonate: diethyl carbonate (3/7 wt ratio). The cells were cycled between 2.5 and 4.2 V (VSP, BioLogic) for rate performance and cyclic performance.
Results
Figure 1 shows the NMC532 performance with various binders from half coin cells. They were similar at low C-rates and were better than that with PVDF from NMP-based processing at high C-rates. The one with latex also demonstrated identical cyclic performance to that with PVDF. This indicates comparable performance could be obtained on NMC532 from aqueous processing.
Figure 2 shows the effect of drying temperature on discharge capacity of NMC. The various drying temperatures lead to different residual moisture. According to Figure 2, NMC532 dried at 120oC for 2 h showed the best performance. The residual moisture was 45 ppm at that condition. The drying condition is similar to that with conventional BMP-based processing. This indicates that it doesn’t require extra effort to remove residual moisture from electrode fabricated via aqueous processing. Aqueous processing of composite cathodes could provide comparable performance to those via conventional NMP-based processing.
Acknowledgment
This research at Oak Ridge National Laboratory (ORNL), managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy Vehicle Technologies Office (VTO) Applied Battery Research 9ABR) subprogram (Program Managers: Peter Faguy and David Howell).
References
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