Electrochemically Manipulating The Redox State Of 2,2’,5,5’-Tetrahydroxybiphenyl As A New Organic Li-Rich Cathode For Li-Ion Batteries

Lithium ion battery is a new kind of energy storage battery developed in the late1970s.It has the characteristics of high voltage,high energy density,long life,high specific capacity and so on.The battery with high capacity and high energy density makes all kinds of electric vehicles and electronic products develop rapidly,which makes great contribution to improve human life.Most of the lithium-ion batteries on the market are made of inorganic materials.In 1980,Goodenough first proposed using Li Co O₂as cathode material for lithium-ion batteries.Although people have done a lot of research on the application of inorganic materials in lithium-ion batteries,it is very difficult to find new inorganic materials and make breakthrough progress in battery performance.However,for organic materials,it is possible to identify kinds of novel organic structures.Because the power density of the battery depends on the reaction kinetics of the material,the reaction speed of organic molecules is faster than that of inorganic molecules,so the power density of organic materials is very high.In this work,a new type of organic electrode material 2,2’,5,5’-tetrahydroxybiphenyl（BP4OH）was first synthesized and used in lithium-ion batteries.At the same time,two kinds of electrochemical methods were in-situ converted to lithium salt（BP4OLi）and the differences in the battery performance are studied.Firstly,the effects of different conductive additives on the BP4OH lithium ion half-cell were explored.It was confirmed that CMK-3 could relieve the dissolution of this organic small molecule to improve the battery performance.Meanwhile,the difference in battery performance under the two different electrochemical methods was compared and analyzed by means of characterization.Second,we continue to synthesize 2,2’,5,5’-tetrahydroxybiphenyl derivatives（p-TP4OH and m-TP4OH）and explore the difference in battery performance in lithium-ion batteries.The results show that p-TP4OH,a derivative of 2,2’,5,5’-tetrahydroxybiphenyl,exhibits better cycle stability in batteries than m-TP4OH.Finally,this work finally selects p-TP4OH as the cathode material and anode material of graphite and Li₂TP respectively to form the full cells.In the graphite II p-TP4OLi,p-TP4OLi can show the peak discharge capacity of 305 m Ah g^-1 and the energy density value of～732 Wh kg^-1.Our work confirms that the Li-rich organic cathodes indeed can fulfill high and comparable energy density with inorganic counterparts after the dissolution problem is well addressed.