The Study On Structural Regulation And Lithium Storage Properties Of Ti-and Co-based Anode Materials For Lithium-ion Batteries

Lithium-ion batteries are widely used in portable electronic devices due to their advantages of high energy density,small self-discharge and no memory effect,and are gradually extended to electric vehicles and efficient energy storage systems.However,in the face of the increasing energy density demand,the development of high-capacity electrode materials is the current research focus.Among them,titanium based anode has a high and stable platform voltage and"zero strain"characteristics,which has attracted wide attention.In addition,cobalt based oxide is also a promising anode material due to its advantages of high capacity and high conductivity.However,the poor intrinsic electron conductivity and lithium ion diffusion rate of Ti-based anode materials lead to poor multiplier performance,while the alloying reaction mechanism of cobalt-based anode materials leads to low first-week charge and discharge efficiency and poor cyclic stability,which limit their large-scale application.This paper from the ratio of titanium electrode material performance and the structure stability of the cobalt electrode material direction,the bipolar symbiotic porous structure and hierarchical structure of titanium anode materials/cobalt base structure and the influence of the electrochemical properties,and discusses the structure regulation of titanium/cobalt electrode materials of electrochemical reaction mechanisms.Firstly,the biphasic symbiotic titanium matrix composite Li₂TiO₃/Li₂MTi₃O₈(M=Zn_1/3Co_2/3)was synthesized by coprecipitates and high-temperature solid phase reaction.The biphasic symbiotic structure was proved by SEM and HRTEM to inhibit the primary grain growth in high-temperature solid phase reaction,and the nanoscale composite was prepared.Cyclic voltammetry?CV?confirmed that the biphasic titanium matrix composite had a significantly improved Li⁺diffusion coefficient(1.24×10^-10cm² s^-1).Therefore,electrochemical tests have shown that biphasic symbiotic nanocomposites have a reversible capacity of 200 mAh g^-1 and discharge voltage of 0.8 V?vs.Li/Li⁺?under the condition of 0.1C charge and discharge process.At the same time,it also has excellent cycle stability?cycle retention rate?100%even after 500 cycles at 0.5C?.In addition,under the condition of 20C high-rate charge and discharge,the dual-phase symbiotic nanocomposite has a reversible capacity of up to 133 mAh g^-1,showing excellent high-rate performance.The biphasic symbiosis strategy can be used as a reference for the grain size control and the multiplier property improvement of titanium base and other anode materials.Secondly,a porous graded spherical Li₄Ti₅O₁₂?LTO?assembled from nanoscale primary grains was prepared by precipitation,dissolution and solid reaction.Due to the dense accumulation of spherical particles,the LTO prepared has a high vibration density of 1.06 g cm^-3,which can improve the volume energy density of lithium ion batteries.At the same time,due to the low specific surface area and small primary grain size of the spherical structure,the Li⁺migration can be improved and the surface side reaction can be reduced,so the LTO has the characteristics of high specific capacity,high stability and high multiplier.More importantly,the full battery assembled with the high nickel layer positive electrode has a reversible capacity of 217.3 mAh g^-1 and a discharge voltage of 2.26 V,corresponding to the energy density of 147 Wh kg^-1.Even at ultra-high power rates of 20C and 50C,the full battery has an energy density of up to 110 and 95 Wh kg^-1.In addition,the lithium ion battery also has excellent cycle stability,with a capacity retention rate of 98.7%after 4000 cycles.Finally,a simple and gentle method was designed and developed to prepare Co O/Co₂B/r GO nanocomposites,in which rGO with high surface area can provide enough fixed sites for nanoparticles,buffer volume expansion and provide conductive matrix during circulation.The CV test confirmed that the proportion of capacitance contribution in the total charge storage of the composite was up to 60%to 90%,which will help to improve the first-cycle coulombic efficiency and structural stability of cobalt-based anode materials.Electrochemical tests showed that the composite had a reversible capacity of 937.3 mAh g^-1and a high first-week coulomb efficiency of 75.28%.The high capacitance contribution also improves the cyclic structural stability of cobalt-based anode materials(the reversible capacity is 574.6 mAh g^-1 after 250 cycles under 0.5C).In addition,highly conductive Co₂B and rGO and nanoparticle coordination effects improve electron/Li+conduction in REDOX reactions and improve the multiplier characteristics of cobalt-based anode materials.This method can be extended to other transition metal oxide anode materials.In this paper,the structure of titanium/cobalt based anode materials is regulated by the design of biphasic symbiosis structure and porous hierarchical structure,and the influence of biphasic symbiosis and porous hierarchical structure on the electrochemical properties and the mechanism of action are studied.