Nowadays, the LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode material has attracted great research interest due to its high energy density and less usage of costly raw materials. However, the high nickel content of NCM811 brings about an extremely unstable interface between the electrode and electrolyte and therefore inferior cyclic stability. Herein, we have proposed a straightforward method to deliver 1, 2, and 4 wt % of TiO 2 nanoparticles (NPs) on the surface of the NCM811 cathode material and to improve its properties at room and high temperatures. Based on scanning electron microscopy and transmission electron microscopy observations, the coating thickness varies from 10 to 35 nm and the 2 wt % TiO 2 -coated cathode is provided with uniformly distributed NPs that could result in an improved structural stability and electrochemical performance. In detail, at 25 and 55 °C and 1 C, the 2 wt % TiO 2 -coated cathode shows capacity retentions of 90.0 and 80.5% after 100 cycles, higher than those of pristine and coated cathodes. Under a high current rate of 10 C at 25 and 55 °C, the discharge capacities of the 2 wt % TiO 2 -coated cathode were 135.9 and 141.4 mA h g −1 , which are significantly higher than those of the pristine cathode material (128.3 and 89.1 mA h g −1 ). Results of the dissolution test at 55 °C reflect the effectiveness of the TiO 2 coating in maintaining the structural integrity of the cathode material and protecting it from HF attack and deleterious side reactions. Also, the differential scanning calorimetry result proves the enhanced safety after surface modification; the TiO 2 coating shifts the exothermic peak of the electrode from 231.1 to 242.9 °C. Therefore, surface modification with TiO 2 NPs can be proposed as a practical and cost-effective method for the commercial application of the high energy density NCM811 cathode at room and high temperatures. KEYWORDS: LiNi 0.8 Co 0.1 Mn 0.1 O 2 , nanocoating, TiO 2 , safety, cathode, lithium-ion batteries

LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) has been considered as a promising cathode for Li-ion batteries (LIBs) due to its high electrochemical capacity and low cost; however, poor cycling stability is one of the main restricting factors in industrial applications of the NCM811 cathode material. Notably, the capacity fading and low structural stability of NCM811 are intensified at elevated temperatures. ZrO 2 -and composite rGO−ZrO 2 -coated NCM811 were fabricated by a facile wet chemical method and evaluated at 25 and 55 °C to overcome these impediments. The ZrO 2 coating provides superior cycling and thermal stability and perfectly protects the cathode active material from deleterious side reactions, and HF attacks by suppressing the direct contact of NCM811 particles and electrolytes. Despite these advantages, the discharge capacity of the ZrO 2 -coated cathode material (166.3, 187.7 mAh g −1 ) is slightly lower than that of the pristine cathode (171.7, 193.0 mAh g −1 ) due to the insulative nature of ZrO 2 NPs, after one cycle at ambient and elevated temperatures. The first cycle discharge capacity increased to 185.9 and 206.7 mAh g −1 at 25 and 55 °C, respectively, with the rGO−ZrO 2 -coated cathode material. The capacity retention reached 92.4 and 83.3%, showing high capacities of 171.8 and 172.3 mAh g −1 at 1C after 100 cycles at 25 and 55 °C, whereas the pristine cathode material exhibited low retention values of 72.4 and 54.5% with discharge capacities of 124.3 and 105.2 mAh g −1 under the same conditions, respectively. The incorporation of rGO into the coating can make up for the ZrO 2 coating imperfection and, at the same time, can enhance the ion/electron conductivity of the electrode by providing a conductive network on the surface of the cathode material. In light of the fact that ZrO 2 -and composite rGO−ZrO 2 -coated NCM811 cathode materials exhibit superior performance; they can pave the way for industrial applications of high-energy-density lithium-ion batteries. KEYWORDS: LiNi 0.8 Co 0.1 Mn 0.1 O 2 , nanocoating, reduced graphene oxide, ZrO 2 , thermal stability, lithium-ion batteries

Improvement of the electrochemical properties of a LiNi0.5Co0.2Mn0.3O2 cathode material by SiO2/reduced graphene oxide double-layer coating.

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