Study On Zirconium And Boron Modification Of Ni-Rich LiNi_0.83Co_0.12Mn_0.05O₂ Cathode Material

As environmental and energy issues become increasingly prominent,new energy materials have become the research hotspot.Lithium-ion batteries have advantages in energy storage,such as low self-discharge,high energy density,high output power,and no memory effect,and are widely used in various fields.As the main component of the lithium ion battery,the cathode material is the key to improve the performance of the lithium ion battery.Among all cathode matterials,the Ni-Rich cathode material is identified as one of the most promising cathode materials.However,with the increase of Ni content,the structure stability of Ni-Rich cathode material becomes worse,which leads to the deterioration of electrochemical performance.In this paper,LiNi0.83Co0.12Mno.05O2 cathode material is used as the research object,and the effect of synthesis temperature on the material properties is studied.In addition,the stability of interface and bulk of LiNi0.83Co0.12Mn0.05O2(NCM)cathode material is further improved through the synergistic effect of coating and doping,and the corresponding electrochemical performances are significantly improved.(1)LiNi0.83Co0.12Mn0.05O2 cathode material was synthesized by a solid state method using commercial precursor and lithium hydroxide as raw materials.The effect of different synthesis temperature on the surface morphology,crystal structure and electrochemical performance of the material was studied,when the synthesis temperature is 760?,the synthesized material has higher discharge specific capacity and better rate performance.In order to further improve the electrochemical performances of the LiNi0.83Co0.12Mn0.05O2 cathode material,based on the above-mentioned definite synthesis process,we added ZrO2 during a lithiation process for a hydroxide precursor,the Zr-modified LiNi0.83Co0.12Mn0.05O2 materials were obtained by mechano-chemical bonding technology and high-temperature calcination,and the Zr-modified cathode materials display excellent electrochemical performances.The morphology,crystal structure and element valence of Zr-modified LiNi0.83Co0.12Mn0.05O2 material were studied with the X-ray diffraction(XRD),energy dispersive spectrometer(EDS),scanning electron microscope(SEM),high-resolution transmission electron microscope(HRTEM)and X-ray photoelectron spectroscopy(XPS).All results show that Zr4+was not only doped into the material,but also a Li6Zr2O7 coating layer was formed on the surface.The Zr4+ doped into lattice can not only form a strong Zr-O bond to stabilize the layered structure,but Zr4+ located in the Li layer can also act as a pillar to maintain the layered structure and reduce the Li+/Ni2+ mixing.In addition,the Li6Zr2O7 coating layer can also play a dual role in promoting Li+ migration and supressing surface side reactions.The synergistic effect of bulk Zr4+ doping and surface Li6Zr2O7 coating together improve the cycle stability of the Ni-Rich material.The electrochemical performances show that the modified material exhibits excellent cycle stability:1%Zr-NCM cathode material still has a discharge capacity of 173.9 mAh g"1 at 1 C after 200 cycles with 2.5-4.3 V voltage range at 25?,corresponding to a capacity retention of 94.6%,the unmodified NCM only delivers 129.9 mAh g-1 with a capacity retention of 68.6%after 200 cycles.(2)Diboron trioxide(B2O3)is introduced to modify the surface of NCM cathode material by a Mechano-Chemical Bonding Technology and at low fire temperature.B2O3-modified NCM shows superior cyclic stability with capacity retention of 87.7%at 1 C between 2.5 V and 4.3 V after 200 cycles in comparison to 69.4%for the unmodified NCM.On the basis of structure and electrochemical characterizations,we concluded that the superior cycle stability of B2O3-modified NCM material benefits from the formation of B2O3 coating layer and B diffusion into the material.The B2O3 coating layer confirmed by the scanning and the transmission electron microscope could suppress the surface side reactions and reduce the content of Li2CO3 on the surface,which can improve the interface stability and safety performance for the modified material.And the B diffusion into the material proved by XRD and XPS triggers partial Ni3+reduction to Ni2+,which enhances the structural stability to a certain extent.Furthermore,the combination of surface B2O3 coating and B diffusion into the material restrains the extension of phase transition and microcrack for NCM material.Such surface modified strategy provides a direction for the acquisition of long-life cathode materials.(3)Combined the zirconium and boron modified characteristics,the ZrB-NCM cathode material was synthesized by a composite modification method.Compared with single zirconium modification,the ZrB-NCM cathode material shows strong structural stability and thermal stability,the main exothermic peak of the ZrB-NCM cathode material is located at 200?,which is higher than the main exothermic peak(168?)for the unmodified NCM.The ZrB-NCM cathode material has a capacity retention value of 99.4%after 100 cycles at 1 C between 2.5 and 4.3 V at 25?,nevertheless the unmodified NCM and Zr-NCM only remain 79.5%and 92.8%of the initial discharge capacity,respectively.XRD results show that the ZrB-NCM cathode material still has the original layered structure after 100 cycles,while the layered structure of unmodified NCM was destroyed.The co-modification strategy can improve the stability of the bulk phase and the interface at the same time,and significantly inhibit the degradation of the electrochemical performances during the long cycles.