H3PO4 treatment to enhance the electrochemical properties of Li(Ni1/3Mn1/3Co1/3)O2 and Li(Ni0.5Mn0.3Co0.2)O2 cathodes

In this study, Li(Ni1/3Mn1/3Co1/3)O-2 (NMC333) and Li(Ni0.5Mn0.3Co0.2)O-2 (NMC532) have been subjected to a phosphoric acid (H3PO4) solution treatment to form a thin Li3PO4 coating on their surfaces. The Li3PO4 coating formed is found to be very potent in enhancing the specific capacity of the first discharge as well as the rate capability and capacity retention in the subsequent charge/discharge cycles for both NMC333 and NMC532. The specific capacity of the first discharge for NMC532 has been increased drastically from similar to 160 mA h g(-1) for pristine NMC532 to similar to 250 mA h g(-1) for Li3PO4-coated counterpart at 0.1C and such a large capacity enhancement is retained throughout the subsequent cycles at 1C. The final specific capacity of Li3PO4-coated NMC532 is 187 mA h g(-1) after 100 cycles at 1C, whereas the corresponding value of pristine NMC532 is only 50 mA h g(-1). The rate capability has also been improved significantly with Li3PO4-coated NMC532 exhibiting similar to 150 mA h g-1 capacity at 6C while pristine NMC532 showing zero capacity. Similar improvements have also been achieved with NMC333. These results demonstrate that the H3PO4 treatment is a facile and general method to improve the electrochemical properties of NMCs with different compositions and can be utilized for practical applications. (C) 2019 Elsevier Ltd. All rights reserved.