| The high nickel ternary cathode material Li Nix Coy Mn1-x-y O2（0.8≤x≤1）is widely used in lithium-ion batteries due to its high energy density,high operating voltage,and cost-effectiveness.However,as the demand for higher energy density increases,high nickel ternary materials face challenges such as reduced cycle stability and rapid capacity decay.One common modification technique is surface coating,which can prevent direct contact between the electrolyte and active material,inhibit surface side reactions,and improve the cycling stability of high nickel ternary materials.However,conventional coating materials often have poor ionic conductivity,which negatively impacts Li+transport,resulting in a decline in the material’s rate performance and increased cell polarization.To address this issue,fast ionic conductors with high ionic conductivity are ideal cladding materials.The fast ionic conductor cladding layer provides a channel for Li+diffusion and stabilizes the electrode/electrolyte interface,ultimately improving the cycling performance and rate performance of high nickel ternary materials.In this study,the high nickel ternary cathode material Li Ni0.83Co0.12Mn0.05O2（NCM83）was modified by a modification strategy of optimizing the surface residual lithium compounds while forming an in situ fast ion conductor cladding layer.The main elements include the following:（1）The precursors were prepared by co-precipitation method,and the high nickel ternary material Li Ni0.83Co0.12Mn0.05O2 was synthesized by high-temperature sintering method,and the optimal firing temperature was investigated.The results showed that when the firing temperature was 750℃,the material crystallized incompletely and the discharge specific capacity was low,while the firing temperature of 810℃led to the abnormal growth of the material particles,which was not conducive to the de-embedding of Li+.It was found that the material synthesized at 780℃exhibited optimal performance,with a first discharge specific capacity of 211.01 m Ah g-1 at 0.1C in the voltage range of 2.8-4.2 V.To further enhance the electrochemical performance,a sol-gel method was employed to coat the cathode material precursors,followed by high-temperature firing to prepare a Li1.5La1.5WO6（LLWO）cladding layer.LLWO,with a high ionic conductivity of 1.38×10-7 S cm-1,was chosen as the cladding material due to its fast Li+transport properties.The morphology,crystal structure,and elemental valence of the resulting material were characterized by XRD,SEM,EDS,XPS,and TEM.The analysis revealed that the surface of NCM83 was uniformly coated with an amorphous LLWO layer,which effectively protected the cathode material from electrolyte erosion and side reactions.The LLWO cladding layer also provided three-dimensional lithium ion channels,which facilitated faster Li+release and insertion,leading to improved cycling and rate performance of the material.Electrochemical testing indicated that the 5 wt.%LLWO-clad NCM83 sample had a discharge specific capacity of 182.71 m Ah g-1 after 100 cycles at 1 C in the voltage range of 2.8-4.2 V,with a capacity retention rate of 92.85%.Furthermore,the rate performance was enhanced to162.80 m Ah g-1 at 5 C,demonstrating a significant improvement compared to the pristine sample,which had a capacity retention rate of 83.21%after 100 cycles and 149.83 m Ah g-1 at5 C.（2）In order to further improve the electrochemical performance of the material,the optimum cladding amount of 5 wt.%was selected in this study,and the crystalline LLWO was compounded with NCM83 using the ball mill compounding method to obtain the NCM83/LLWO cathode composite.The results showed that the composite of LLWO improved the cycling performance and rate performance of the material.NCM83/LLWO sample exhibited a discharge specific capacity of181.23 m Ah g-1 after 100 cycles at 1 C with rate performance of 160.09 m Ah g-1 at 5 C.There were some differences in the performance of the LLWO composite sample compared with the LLWO clad sample.This may be due to the better structural compatibility of the amorphous LLWO cladding layer in the clad samples,while the ball milling composite process of NCM83/LLWO leads to problems such as material structural damage and uneven material dispersion,which results in a degradation of performance.（3）In comparison to LLWO,the fast ionic conductor Li1.5La1.5Te O6（LLTe O）exhibits a higher ionic conductivity(9.28×10-7 S cm-1)and more stable chemical properties.Therefore,the surface coating of NCM83 was studied using different amounts of amorphous Li1.5La1.5Te O6.The test results indicated that a coating layer with a thickness of approximately 5 nm was formed on the surface of NCM83.The LLTe O coating reduced the specific surface area of the cathode material,inhibited surface side reactions,enhanced the structural stability of the material while promoting Li+transport,ultimately leading to improved electrochemical performance of NCM83.The Li+diffusion coefficient increased from 8.757×10-12 cm2·s-1 to 2.967×10-11 cm2·s-1 after coating.After 100 cycles at 1 C,the capacity retention of NCM83-0.05LLTe O increased from 86.23%to 91.85%,and after100 cycles at 3 C,the capacity retention increased from 83.22%to 88.97%.Moreover,the highest specific discharge capacity of 165.40 m Ah g-1 was achieved at 5 C with a large rate discharge.（4）the sol-gel method was used to coat NCM83 with a fast ionic conductor,Li0.33La0.56Ti O3（LLTO）,which has a higher ionic conductivity of 1.00×10-3 S cm-1.The effect of crystalline LLTO coating on the structure and electrochemical performance of NCM83 was investigated.The results showed that an LLTO coating of about 2 nm could improve the cyclic and rate performances of the material by suppressing side reactions and promoting Li+transport.NCM83 coated with 5 wt.%LLTO showed excellent rate performance and cycle stability.After 100 cycles at 1 C within the voltage range of 2.8-4.2 V,NCM83-0.05LLTO exhibited a discharge capacity of 185.9 m Ah g-1,with a capacity retention rate as high as 91.24%.In particular,at a high rate of 5 C,the discharge capacity of LLTO-coated NCM83 was 162.38 m Ah g-1,corresponding to a capacity retention rate of 81.2%at 0.2 C. |
