The Electrochemical Performance of The Blended Cathode of LMFP and NMC811

Blended cathodes are one of new approach for enhancing both characteristics of different cathode active materials. In previous study, a blended cathode between olivine structural cathode active materials and layered lock salt cathode active materials are applied to lithium ion cell to realize high thermal stability derived from olivine and large capacity derived from layered rock salt type. The blended cathode between lithium iron phosphate (LFP: LiFePO 4 ) and lithium nickel cobalt manganese oxide (NMC 1-x-y, x, y : LiNi 1-x-y Mn x Co y O 2 ) shows a high stability of crystal structure and large specific capacity. However, an operation voltage of LFP and NMC is 3.3 V and 3.8 V, respectively. The difference in their operation voltage leads to a poor performance of cathode. Recently, lithium manganese iron phosphate (LMFP: LiMn 1-x Fe x PO 4 /C) has been expected as a excellent cathode active material due to higher operation voltage and higher energy density than those of LFP. LMFP is prepared by a replacing of Fe by Mn in LFP. The Mn 2+ /Mn 3+ redox can be used, leading to higher operating average voltage of 3.8V with high stability of ordinary olivine structure features (high stability, capacity:170 mA h g -1 , long cycle performance). Therefore, the blended cathode between LMFP and NMC has been expected as a new cathode with high performances. The cathode performance depends on the blending ratio between LMFP and NMC. The effect of blending ratio on cathode performance have been reported in previous study. Various NMCs has been widely used as a cathode active material. Recently, a lithium ion battery using high nickel NMC811 cathode have been actively studied, due to its high specific capacity. However, NMC811 cathode has a low thermal stability due to weak chemical bond between Ni and O, elution of Ni and Mn in an electrolyte and a crack formation due to volume expansion and shrinkage during charge and discharge cycles. These problems have to be solved to realize lithium ion battery with NMC811 cathode. In previous study, Both LMFP and NMC cathodes have been made by solid-state process. The blended cathode using cathode active materials made by solid-state reactions shows a concern in a sense of a cathode layer density. In this study, physical properties and electrochemical performance of the blended cathode between LMFP made by hydrothermal-synthesis and NMC811 made by solid-state reaction were investigated by using laminated cells at room and high tem