Preparation And Lithium Storage Capabilities Of Ni-Mn-based High Voltage Cathode Materials For Lithium-ion Batteries

The rapid development of electric vehicles and hybrid electric vehicles requires high-performance lithium-ion batteries materials?LIBs?,but the existing LIBs do not meet the increasing need for endurance and cost.A large number of novel negative materials with high energy density and power density have been studied.However,the specific capacity of the current cathode materials cannot match the anode materials.Therefore,searching for the cathode materials with high specific capacity is critical for high-performance LIBs.In this paper,the high-voltage cathode material was prepared by wet ball milling followed by high temperature heat treatment,and the material was modified with the main problem of the material.The contents and results of the study are as follows:?1?A series of xLi₂MnO₃·?1-x?LiNi_0.5Mn_0.5O₂?x=0.3,0.4,0.5 and 0.6?single crystals is successfully synthesized via wet mechanical ball milling.At 0.1 C current rate,the 0.4LMO sample delivers 212 mAh g^-1 after 100 cycles,much higher than the value of 0.3LMO and 0.6LMO.The results show that the specific capacity and cycle stability of xLi₂MnO₃·?1-x?LiMn_0.5Ni_0.5O₂ samples depend on the synergistic effect of Li₂MnO₃ and LiNi_0.5Mn_0.5O₂ components.?2?Li_1.147K_0.026Mn_0.582Ni_0.25O₂?LKMNO?sample is successfully prepared by doping K⁺ions into Li slab.LKMNO sample delivers the capacities of 160.2 and 135.1mAh g^-1 at 1 and 5 C rates,respectively,but LMNO sample only delivers 135.1 and 0mAh g^-1.The effects of K⁺doping on the relationship between the charging-discharging process and phase change are detailed studied by the incremental capacity curves?dQ/dV?at the various cycles.K⁺doping in LKMNO sample plays an essential role in rate performance and cyclic performance,because it effectively hinders the formation of spinel structure and stabilizes the hostlayered structure.In the full cell state?pouch cell?,the discharge capacity of LKMNO is 194.6 and 115.4 mAh g^-1 at 0.1 and 1 C rates those are much higher than LMNO for 175.5 and 79.7 mAh g^-1.?3?A series of K-doped Co-free materials Li_1.167-xK_xMn_0.583Ni_0.25O₂?x=0,0.025,0.05 and 0.075?was successfully prepared by ball mill and solid-state sintering method.Compared with the previously reported hydrothermal method,the ball milling and solid-state sintering method can accurately control the content of K⁺doping.The crystal structure,morphology,valence state of surface elements and electrochemical properties of the materials are systematically studied.XRD,SEM shows that the doping of potassium has no obvious change in the structure and morphology of the material.XPS analysis showed that K⁺could induces the formation of Mn³⁺,and excess Mn³⁺results in serious side reactions,so the electrochemical performance does not increase monotonously with the increase of potassium content.For example,at 5 C rate,the discharge capacities are 54.0,108.9,110.1 and 63.9 mAh g^-1 for the LMNO,LK1MNO,LK2MNO and LK3MNO samples after 200^th cycles,respectively.The corresponding capacity retention efficiency is 71.25%,94.94%,95.0%and 55.42%,respectively.The main reason is that a small amount of potassium can expand the interlayer spacing of lithium,increase the diffusion coefficient of Li⁺,reduce the diffusion barrier of Li⁺and stabilize the layered structure.?4?The precursors of LiMn_1.5Ni_0.5O₄?LNM?are respectively synthesized by dry and wet ball-milling.Under wet ball-milling,the problem of sticky residue in dry ball-milling is effectively resolved,the three raw materials form homogeneous slurry and mix well in micrometers level.At 0.1 C rate,LNM-w12 delivers the capacity of 133mAh g^-1 at the 100^th cycle.The great rate capability of LNM-w12 can be attributed to the well-formed crystal structure,ordered and stable surface structure,which is conducive to the diffusion of lithium ions and prevents the dissolution of the material at high voltage.