Constructing High Conductive Composite Coating with TiN and Polypyrrole to Improve the Performance of LiNi_0.8Co_0.1Mn_0.1O₂ at High Cutoff Voltage of 4.5 V

LiNi0.8Co0.1Mn0.1O2, one of the typical nickel-rich cathode materials, is considered as a candidate for next generation high energy density Lithium-ion batteries (LIBs) due to its high specific capacity and relatively low cost. But there are still some issues, such as poor cycling performance and thermal stability, to be addressed when charging the nickel-rich cathode materials for LIBs to high cutoff voltage. Therefore, we construct a multifunctional mixed conductive coating layer with polypyrrole and nano titanium nitride particles to improve the comprehensive performance of LiNi0.8Co0.1Mn0.1O2, especially the rate performance and the thermal stability. This mixed coating layer not only inhibits the side reactions at the interface of the active material but also possesses high conductivity as well as the unique elasticity that can release the stress of the cathode during cycling. Comparing with the single polypyrrole coating layer, such a mixed coating layer can ensure the comodified LiNi0.8Co0.1Mn0.1O2 maintaining 80.1% capacity retention after 450 cycles at the upper cutoff voltage of 4.5 V. Besides, it also alleviates the collapse of the secondary particles after long cycles due to its unique elasticity. Meanwhile, the titanium nitride with super high electronic conductivity greatly improves the conductivity of the comodified LiNi0.8Co0.1Mn0.1O2 so that it can still deliver a specific capacity of 102 mAh·g–1 at 20C. What’s more, the thermal stability of the comodified sample is also improved due to the good thermal conductivity and thermal stability characteristics of the titanium nitride as well as the polypyrrole layer. All the results verify that this design is an effective way to enhance the comprehensive properties of Ni-rich cathode materials.