Crucial role of thioacetamide for ZrO2 coating on the fragile surface of Ni-rich layered cathode in lithium ion batteries

Abstract

Thioacetamide (TA) is essentially introduced to form a ZrO2-coating in a facile method via washing with a Zr(SO4)2 aqueous solution. This method is specially applied for a Ni-rich layered oxide LiNi0.82Co0.09Mn0.09O2 (NCM82), the surface of which is chemically fragile due to unstable Ni3+ ions. Under acidic conditions due to sulfate anions, TA plays a pivotal role in preserving the fragile surface of the Ni-rich layered oxide and leads to a homogeneous coating. With the TA-supported ZrO2 coated sample, the cyclability reaches 89.4% showing a high capacity of 174.0 mAh g−1 at 0.3 C after 100 cycles, whereas the conventional ZrO2-coated sample without TA, which is generally known to be excellent for other positive electrode materials, is a low value of 64.2% with 125.7 mAh g−1 under the same condition. The TA-supported ZrO2-coated layer is notably homogeneous and has a thickness of approximately 5.75 nm. In addition, the TA-supported ZrO2-coated cathode material also displays a greatly enhanced rate capability of 116.8 mAh g−1 under a current density of 3.0 C. The structure of the ZrO2-coated cathode particle prevents unfavorable side reactions on the surface, and therefore, no micro-cracking into the grain boundary occurs after charging/discharging. The titration method demonstrates the removal of a large amount of lithium impurities from the surface of the active material.