Preparation And Performance Study Of Cathode Prelithiation Additive In Lithium Ion Batteries

In recent years,great progress has been made in the research of lithium-ion batteries.The specific capacity,cycle stability and rate performance have been improved,but there are still many problems.Among them,the first irreversible capacity loss limits the application of many high-energy materials,and the first irreversible capacity loss mostly comes from the active lithium consumed by the formation of solid electrolyte interface（SEI）on the anode surface during the first charging process.Adding a new lithium source to the cathode is an effective way to compensate the first irreversible capacity loss.lithium-rich compounds,nanocomposites based on conversion reactions and binary compounds are the main materials that can be used as cathode prelithiation additives.These materials have their own advantages as cathode prelithiation additives,which point out the direction of research and development in related fields,but there are also some defects.most of the lithium-rich compounds are not stable in the air;the nanocomposites based on conversion reactions will form inactive residues after lithium removal,reducing the energy density of the battery;although there is no residue of binary lithium compounds after lithium removal,the released gases,such as O₂ and N₂,will cause capacity degradation and safety problems for the battery.In view of the above problems,this paper explores two new cathode prelithiation additives to compensate for the first irreversible capacity loss of lithium-ion batteries.Firstly,lithium nickel oxide(Li_0.79Ni_1.21O₂)was successfully prepared by high-temperature calcination,which was used as cathode prelithiation additive for Li Ni_0.5Mn_1.5O₄/graphite full cell.Li_0.79Ni_1.21O₂ has a prelithium capacity of about 163 m Ah/g between 3.0 V and 4.7 V.Li_0.79Ni_1.21O₂ is added to Li Ni_0.5Mn_1.5O₄ at a ratio of 1:10 to prepare the mixed cathode,and then the cathode and graphite anode are matched and assembled into a full cell.Compared with the full cell without Li_0.79Ni_1.21O₂ as cathode prelithiation additive,the full cell has more excellent electrochemical performance.The specific discharge capacity of the first cycle is increased by about 14 m Ah/g,and the initial coulomb efficiency is increased from 89% to 98.57%.Li_0.79Ni_1.21O₂,as a cathode prelithiation additive,has successfully compensated the irreversible capacity loss caused by the formation of SEI on the graphite anode surface of lithium-ion battery.Compared with other lithium-rich compounds,Li_0.79Ni_1.21O₂ has more excellent chemical stability in the air.Then we successfully synthesized 3,4-dihydroxybenzonitrile dilithium salt（Li₂DHBN）through a simple chemical reaction in argon atmosphere,and explored its prelithium performance as a cathode prelithiation additive.Li₂DHBN produced up to 307 m Ah/g prelithium capacity between 3.0 V and 4.7 V.We selected NCM as the cathode,added Li₂DHBN at the ratio of 1:10 to NCM to prepare the mixed cathode,and then matched the mixed cathode with the Si Ox anode to form the full cell.Compared with the full cell without Li₂DHBN,the full cell has more excellent electrochemical performance.In the potential range of 2.8 V-4.5 V,the first cycle discharge specific capacity increases by 20 m Ah/g,and the first cycle coulomb efficiency increases from 79% to 91%.The active lithium produced by the additive Li₂DHBN during the first charge successfully compensated for the irreversible capacity loss of the full cell.According to the EIS results,the electrochemical impedance of the full cell decreased significantly by adding Li₂DHBN additive,which was caused by the dissolution of the organic residues.As a cathode prelithiation additive,Li₂DHBN would not have an adverse effect on the dynamic performance of the battery.In addition,compared with inorganic additives,organic lithium supplements have the advantages of low cost,environment-friendly and can be designed at the molecular level.