Terbium Compound Doped Lithium Transition Metal Oxide Cathode

Lithium-ion batteries have been widely used in consumer electronics,energy storage,and electric vehicles since their commercialization.Nonetheless,there is still potential for advancement in the energy density of current commercial lithium-ion batteries.Among the various components used in lithium-ion batteries,the cathode material is critical for limiting energy density and controlling battery costs.The development of high-voltage and high-capacity cathode materials is essential for significantly enhancing the energy density of batteries.Lithium transition metal oxide cathode materials,such as Li Co O₂,LiNi_1-x-yCo_xMn_yO₂（NCM,0<x,y<1）,x Li₂MnO₃·（1-x）Li MO₂（0<x<1,M=Ni,Co,Mn etc.）and LiNi_0.5Mn_1.5O₄,have drawn the interest of scientists due to their distinctive electrochemical activity.The microstructural instability of these cathode materials in a high delithiation state has a significant impact on battery cycle life and presents safety concerns.This thesis suggests the introduction of rare earth terbium ion and phosphate ion as structural stabilization units of lithium transition metal oxide cathode materials to solve this issue.We also investigate the electrochemical property using spectroscopy,microscopy,and theoretical calculations,reveal the synergistic effect of doping elements on the structure and performance of the materials,and eventually improve the energy density and cycling stability of cathode material.The main study contents and results are as follows:1.One or more of ZnO,Y₂（CO₃）₃,Tb₂（CO₃）₃and（NH₄）₂HPO₄are used,to mix with Co₃O₄and Li₂CO₃and then heating at high temperature to obtain doped Li Co O₂（LCO）cathode materials.It is discovered that multi-element co-doping can inhibit irreversible phase transitions of high voltage LCO while maintaining crystal structure stability during the charging and discharging process.Furthermore,density functional theory（DFT）calculations demonstrate Tb element doping can reduce the oxygen activity of LCO upon deep delithiation.The electrochemical performance results show that the capacity retention of Zn-Y-Tb co-doped LCO at high voltage is higher than that of undoped LCO,Zn/Y/Tb single and double element doped LCO,indicating a more superior cycling performance and rate capability.The terbium and phosphate ions co-doped LCO exhibit the best long-cycle stability.The Zn-Y-Tb ternary and Tb-PO₄dual doped LCO exhibit 164.9 m Ah g^-1and 174.7 m Ah g^-1after300 cycles at a cut-off voltage of 4.55 V and a current density of 0.5C,respectively,with corresponding capacity retention of 87.6%and 97.7%,which is substantially higher than the 52.6%capacity retention of the undoped LCO.2.Yttrium/terbium cation and phosphate anion co-doped LiNi_0.83Co_0.11Mn_0.06O₂cathode materials are obtained by mixing Ni_0.83Co_0.11Mn_0.06（OH）_2,LiOH·H₂O and YPO₄/Tb₂（CO₃）₃/（NH₄）₂HPO₄via high temperature reaction in oxygen atmosphere.The chemical reactivity of the materials show that yttrium/terbium elements can stabilize the lattice oxygen of the high nickel cathode material,while the PO₄polyanion has a good affinity for lithium ions,which can accelerate the diffusion of lithium ions in the material.Theoretical calculations reveal that terbium can inhibit the redox activity of oxygen of the material in the deeply delithiated state,thus alleviating the structural degradation.Therefore,the introduction of appropriate content of cations and anions can considerably improve the electrochemical performance of high nickel materials by stabilizing their layered structures and preventing structural collapse during cycling.The discharge specific capacitiy of Y/Tb-PO₄co-doped LiNi_0.83Co_0.11Mn_0.06O₂is 179.9 m Ah g^-1（98%capacity retention）and 179.3 m Ah g^-1（96%capacity retention）after100 cycles at 1C in voltage range of2.7-4.35 V,respectively.And its cycling stability at higher cutoff voltage（4.5 V）is also significantly improved（86.8%and 91.6%capacity retention after 100 cycles at0.5C,respectively）.This strategy is straightforward and manageable,and it has the potential to significantly improve the structural and cycling stability of high nickel layered cathode material.3.TbPO₄-doped Li_1.2Mn_0.52Ni_0.2Co_0.08O₂（LLO523）and Li_1.2Mn_0.54Ni_0.13Co_0.13O₂（LLO111）lithium-rich materials are synthesized via high temperature reaction by mixing Ni_0.25Co_0.1Mn_0.65CO₃/Ni_0.16Co_0.16Mn_0.68CO₃precursor,LiOH·H₂O and TbPO₄homogeneously.It is found that TbPO₄doping could inhibit the degradation of the layered structure caused by the loss of oxygen in the lattice,which can significantly improve the first discharge specific capacity and coulombic efficiency of the Li-rich Mn-based cathode materials,alleviate the decay of potential,suppress the growth of polarization and impedance,and improve cycle stability and rate performance.The discharge specific capacities of LLO523 and LLO111 cathode materials doped with a certain amount of TbPO₄are 204.1 m Ah g^-1and 229.5 m Ah g^-1after 100 cycles at0.5C,corresponding to 96.1%and 98.7%capacity retention,respectively,which are significantly higher than those of the associated undoped samples after cycling.4.The TbPO₄-doped LiNi_0.5Mn_1.5O₄cathode materials are obtained by mixing Ni_0.25Mn_0.75CO₃precursor,LiOH·H₂O and TbPO₄in a certain ratio and then reacting at high temperature.It is found that the effect of terbium and phosphate co-doping on lithium transition metal oxide cathode materials is universal,which can not only enhance the electrochemical performance of cathode materials with layered structure,but also improve the cycling stability of the spinel-type structure LiNi_0.5Mn_1.5O_4.The electrochemical performance results show that LiNi_0.5Mn_1.5O₄doped with appropriate content of TbPO₄exhibits excellent electrochemical performance with a discharge specific capacity of 125.1 m Ah g^-1after 200 cycles at 0.5C（capacity retention:92.3%）and still show a discharge specific capacity of 112.4 m Ah g^-1after 600 cycles.This technique can also provide innovative insights into how to enhance the electrochemical properties of other cathodes with different compositions and structures.