Surface Modification And Research On Electrochemical Performance Of Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ For Lithium-ion Battery

With the development of advanced technology,new consumer electronic devices,drones,and new energy vehicles have increased requirements for the overall performance of lithium-ion batteries.High nickel layered oxide（Li Ni_xCoy Mn_zO₂）is expected to replace Li Fe PO₄ and Li Co O₂ as the next-generation commercial cathode material due to its high energy density and low cost.This article improves the electrochemical performance and storage stability of lithium-ion batteries by improving the synthesis process of Ni-rich NCM and surface coating modification.Simultaneously,the surface coating modification also broadens the working voltage and using temperature of the Ni-rich NCM,so that the battery can keep working in extreme environments.At the same time,the experiment of all-solid-state lithium-ion batteries will provide data contribution for the realization of the next generation of lithium batteries.In this paper,by the structural analysis,micro-region observation,electrochemical performance test and model analysis on pristine Ni-rich NCM and modified NCM confirmed that the improvement of the synthesis process and the modification of the surface coating effectively improved the comprehensive performance of Ni-rich NCM.Furthermore,the paper also analyzes the reasons for its performance improvement.This paper has reference significance for the development of the high-performance Ni-rich NCM cathode materials and Ni-rich NCM interface modification.The research content of this paper is as follows:（1）The gradient method was used to explore the best stoichiometric ratio of Ni_0.8Co_0.1Mn_0.1（OH）₂ and Li OH·H₂O and the best sintering temperature.Hereafter,through data analysis,we summarized the best synthesis conditions of Ni-rich NCM.With this synthesis condition,the Ni-rich NCM has the smallest mixed Li/Ni cation and the best layered structure.With the best synthesis condition,the efficiency of Ni-rich NCM is 82%at the first cycle.Furthermore,the discharge specific capacity after 200 cycles is 145.5m Ah g^-1,with a capacity retention rate of 78.2%.（2）We construct a composite multifunctional coating of CNTs with high electronic conductivity and Li₃PO₄ with high ion conductivity on the surface of Ni-rich NCM.This method not only reduces the residual lithium on the surface of Ni-rich NCM particles,but also improves the mobility of electrons and ions.The multifunctional coating improves the cyclic stability,thermal stability and storage stability of Ni-rich NCM.Ni-rich NCM with LPO-CNT coating has a efficiency of 85.1%at first cycle.With a voltage range of 3.0-4.3V,it still has a discharge specific capacity of 171.2m Ah g^-1 after 500 cycles.CNT-LPO-NCM has a capacity retention rate of 63.9%at high rate（10C）.Ni-rich NCM was exposed to high humidity air for storage stability test,and the specific discharge capacity was 157.1m Ah g^-1after 500 cycles.In addition,Ni-rich NCM was also tested for cycle stability with extreme conditions.The experimental results show that it still has a capacity retention rate of 68.6%after 500 cycles with a voltage range of 3.0-4.5V,while the effect of Ni-rich NCM with LPO-CNT coating is not ideal at high temperature.（3）In order to solve the problem that the multi-functional coating is easy to crack and fall off at high temperature,we constructed a three-dimensional polymer coating.Using UV light irradiation,the Ppy monomer and citrus nitrile monomer were self-assembled on the surface of Ni-rich NCM to construct a polymer coating with electronic conductivity and ion conductivity.The characteristic of polymer coating is able to improve the cyclic stability of Ni-rich NCM at high temperature.Citrus nitrile with two pairs of carbon-carbon double bonds can be polymerized into a network cross-linked polymer,so that the PPC coating will not swell and dissolve in the electrolyte.The polymer coating can effectively suppress the irreversible phase change of the Ni-rich NCM and improve the cycling stability of the lithium ion battery.The specific discharge capacity of NCM811@PPC is 145.2m Ah g^-1 after500 cycles at a current density of 0.5C in the 3.0-4.3V.After assembling the NCM811@PPC into an all-solid-state battery,the PPC coating reduces the interface impedance between Ni-rich NCM and the polymer solid electrolyte,and increases the mobility of electrons and ions at the interface.The NCM811@PPC（all-solid-state battery）first-cycle has efficiency is89.6%with discharge specific capacity of 208.8m Ah g^-1,respectively.Improving the first-cycle efficiency is also one of the methods to increase the energy density of lithium ion batteries.