Stabilizing Effect Of Praseodymium Phosphate And Yttrium Phosphate On The Electrochemical Performance Of Layered Cathode Materials

Lithium-ion batteries（LIBs）have been widely used in energy storage devices and electric vehicles owing to their unique characteristics.With the development of society,the strong demand for energy density is gradually increasing.Although raising the cut-off voltage can be an effective strategy to achieve a higher energy density,the structural instability of layered cathode materials under high cut-off voltages leads to unsatisfactory electrochemical performance and poor cycle life.In addition,the development of low-cobalt or cobalt-free cathode materials for lithium-ion batteries has became a future trend due to the environmental and cost issues.Based on the above situation,two rare-earth metal phosphates,Pr PO₄and YPO₄,are used to modify Li Co O₂,Li Ni_0.6Co_0.2Mn_0.2O₂and Li_1.2Mn_0.56Ni_0.16Co_0.08O₂through a facile solid-state method.The morphology,structure and electrochemical performance of the obtained materials are characterized and analyzed using XRD,XPS,SEM,TEM,CV,EIS and discharge/charge tests.The stabilizing effect of YPO₄and Pr PO₄on the structure and electrochemical performance of the layered cathode materials is also discussed in detail.1.A series of Pr PO₄-modified Li Co O₂cathode materials are prepared by solid-state reaction in air atmosphere using Li₂CO₃,Co₃O₄,and Pr PO₄as raw materials.It is found that Li₃PO₄and Pr Co O₃originated from Pr PO₄at high temperatures are uniformly distributed in the prepared cathode materials.The synergistic stabilizing effect of Pr Co O₃and Li₃PO₄on the Li Co O₂interface promotes the structural stability and electrochemical performance.The Pr PO₄-modified material exhibits a discharge capacity of 171.1 m Ah g^-1after 100 cycles at 4.55 V and 0.5 C,with a capacity retention of 92.5%.Moreover,its reversible capacity reaches 128m Ah g^-1at 5 C,showing significant improvement in electrochemical performance compared to bare Li Co O₂.This work provides an effective method and idea to solve the structural instability of Li Co O₂at high cut-off voltages.2.Li Co O₂materials modified with different proportions of YPO₄are prepared by solid-state reaction in air atmosphere using Li₂CO₃,Co₃O₄,and YPO₄as raw materials.Results show that Li₃PO₄and Y₂O₃derived from YPO₄are uniformly distributed in the particle.The regulation of the crystal cell by YPO₄and the formation of Li₃PO₄/Y₂O₃not only enhance the structural stability of the material,but also avoid the cobalt consumption in the modification.Thus,the long-term cycling performance of Li Co O₂is significantly enhanced by YPO₄modification.The optimized YPO₄-modified Li Co O₂material shows a capacity of 171.6 m Ah g^-1at 0.5C after 500 cycles under 4.55V,with 91.7%capacity retention.And a discharge capacity of 145.3 m Ah g^-1at 5 C is also achieved for Li Co O₂.In this work,the YPO₄-modified Li Co O₂materials exhibit excellent electrochemical performance at4.55 V,and the method involved has the advantages of simplicity,practicality,and abundant material sources.3.YPO₄-modified Li Ni_0.6Co_0.2Mn_0.2O₂materials are prepared by solid-state reaction at high temperature in an oxygen atmosphere using Li OH,Ni_0.6Co_0.2Mn_0.2（OH）₂,and YPO₄as raw materials.The obtained materials are spherical secondary particles with a particle size of about 10μm.It is found that Li₃PO₄and Li YO₂caused by the YPO₄modification are uniformly distributed on the surface of primary particles.Li₃PO₄and Li YO₂effectively enhance the interface stability of primary particle,suppress the Li⁺/Ni²⁺disorder during the cycling process,and finally lead to the improved structural stability and electrochemical performance.The YPO₄-modified Li Ni_0.6Co_0.2Mn_0.2O₂material exhibits a capacity of 134 m Ah g^-1at 1 C after 300 cycles under 4.5 V,corresponding to a capacity retention of 80.0%.This work verifies that YPO₄modification can effectively improve the high-voltage cyclic stability of low-cobalt high-nickel cathode materials.4.Precursor Mn_0.7Ni_0.2Co_0.1CO₃is prepared by a co-precipitation method using transition metal sulfates and Na₂CO₃as raw materials.Li_1.2Mn_0.56Ni_0.16Co_0.08O₂materials modified by Pr PO₄are obtained by mixing Li OH,Mn_0.7Ni_0.2Co_0.1CO₃and Pr PO₄thoroughly,followed by the high-temperature calcination.The obtained materials are secondary particles with a quasi-spherical morphology,and the particle size is about 10μm.Li₃PO₄and Pr_0.96Mn_0.982O₃derived from Pr PO₄are distributed on the surface of primary particles.The Pr PO₄modification improves the initial coulombic efficiency of material.Moreover,the presence of Li₃PO₄/Pr_0.96Mn_0.982O₃enhances the interface stability of primary particle and suppresses the detachment of primary particles from secondary particles during the cycling process.Therefore,the structural stability and electrochemical performance of the material are reinforced by Pr PO₄modification.The Pr PO₄-modified Li_1.2Mn_0.56Ni_0.16Co_0.08O₂material exhibits a reversible capacity of 195.1 m Ah g^-1with a capacity retention of 91.8%after 200 cycles at 0.5 C under4.8 V.This work verifies that rare-earth metal phosphates can enhance the electrochemical performance of low-cobalt lithium-rich manganese-based materials,providing a reference for improving the electrochemical performance of cobalt-free cathode materials at high voltages.