Effect Of Novel Conductive Additives On The Performance Of Cathode Materials For Vehicle Power Batteries

Granular conductive carbon black（such as Super P,acetylene black,etc.）commonly used in commercial lithium-ion batteries is characterized by low density,easy agglomeration and low utilization.Moreover,the"point to point"conduction mode is difficult to form a good conductive network between the cathode particles.In order to ensure the conductive effect,the amount of conductive carbon black should be increased,which will in turn reduce the energy density of the batteries.Therefore,developing alternative conductive additives with high conductivity,while reducing the use of conductive additives,can not only improve the conductivity of the electrode,but also increase the load of active materials,thereby increasing the power and energy density of Li-ion batteries.Graphene and carbon nanotubes（CNTs）,as high conductive carbon materials,are ideal candidates for new conductive additives for lithium ion batteries.However,for different sizes and different kinds of electrode materials,the effect and mechanism of conductive enhancement are not the same,and the related research is still scarce.Herein,the effects of different dimensions of conductive additives on the electrochemical properties of two cathode materials,LiNi_0.8Co_0.15Al_0.05O₂（NCA）and LiCoO₂（LCO）with different particle sizes were studied.The objective is to obtain optimized graphene,CNTs and Super P（SP）composite conductive agents to improve the rate performance and cyclic stability of cathode materials.Furthermore,the composite conductive additive was used to prepare mixed cathode materials of NCA and LCO in order to obtain lithium ion batteries with high operating voltage and good electrochemical performance.The main achievements of this paper are as follows:1.Nano-scale NCA cathode materials were studied by using graphene,CNTs and SP as different conductive agents.When 0.5G-1CNTs-0.5SP ternary mixture conductive was used,a multi-scale composite conductive network was formed on the surface of NCA particles to achieve the optimal electrochemical performance.The specific capacity(148 mA h·g^-1)at 10 C(1C=200 mA·g^-1)current density was 70.5%when at 0.2 C,and the capacity retention rate at 1C current density after 100 cycles was 88.6%.However,when 1G-1SP is used as conductive agent,excessive graphene has a steric hindrance on nano-scale cathode materials,which will hinder the diffusion of lithium ions,resulting in poor rate performance and cycle stability.2.The effects of different conducting agents on the properties of LCO cathode materials were studied.When graphene content is high,there is no obvious hindrance to lithium ion transport as NCA system.This is because graphene sheet is semi-coated on LCO particles,which reserves diffusion channels for lithium ions.When 0.5G-1CNTs-0.5SP ternary conductive agent is used,the optimal electrochemical performance is achieved.The specific capacity(118.2 mA h·g^-1)at current density of 10 C(1 C=140 mA·g^-1)is 78.0%when at 0.2 C,and the capacity retention rate at 1 C after 100 cycles is 92.3%.3.NCA and LCO were mixed by mechanical milling according to different mass ratio,and0.5G-1CNTs-0.5SP was used as conductive additive,and the electrochemical performance was tested.The results show that adding a certain amount of LCO into the NCA cathode material can improve the working voltage and reduce the internal resistance.When LCO:NCA=5:5,the specific capacity(140 mA h·g^-1)at 10 C(1 C=140 mA·g^-1)current density was 77.5%when at0.2C,and the capacity retention rate at 1 C after 100 cycles was 89.7%.Compared with pure NCA,hybrid cathode materials have better rate performance and cycle stability,and higher specific capacity than pure LCO.