Reuse Of LiMn₂O₄ Cathode Materials In Spent Lithium Ion Batteries

Lithium ion batteries?LIBs?play an important part in today's highly electrified world and will continue to lead technological innovation.However,the wide application of lithium ion batteries will cause a large number of spent batteries,which have the dual characteristics of environmental risk and resource utilization value.On the one hand,there are plenty of heavy metal and fluorine-containing electrolytes in spent batteries,which will be harmful to human bodies and pollute the environment if they are released into the environment without proper treatment.On the other hand,there are many metals including Ni,Co,Mn,Cu and Li which are limited resources in the earth,and can be recycled and have resource value.Therefore,the recycling of lithium ion batteries attracts the academia and industry to develop a variety of technologies to minimize the risks,maximize benefits,and ultimately achieve “waste-to-wealth”.There are two ways to dispose of spent lithium ion batteries: trapezoidal utilization and recycling.Cathode materials often have a higher metal value,so recycling them is a better way than using them for cheaper energy storage.Meanwhile,sodium ion batteries?SIBs?have been considered as one of the most promising alternatives to LIBs in the past few years due to the abundance of sodium in the earth,low price,and similar chemical properties to lithium.In the thesis,the main object is the cathode materials of spent LiMn₂O₄ batteries.There are two strategies to achieve the reusing of recycled LiMn₂O₄,details as follows:?1?The recycled LiMn₂O₄ is directly used as positive electrode material in SIBs to study its electrochemical performance,structure evolution,and electrode kinetics.Specifically,the initial discharge specific capacity of recycled LiMn₂O₄ electrode is 90.7 mAh g^-1at 100 mA g^-1?1.1C?,the discharge capacity increases to 163.2 mAh g^-1after 50 cycles,and the capacity retention is 97.6% after 200 cycles.And the reversible capacity is up to 176.3 mAh g^-1at 20 mA g^-1.Electrochemical analysis and a series of ex-situ characterizations explain that the continuous increase of capacity in the first 50 cycles is the?de?insertion of Li⁺/Na⁺ resulting in the transformation of spinel into a layered structure.In addition,the results of the electrode kinetics show that the diffusion rate of ions in layered materials is faster than that in spinel.This work not only reveals the structural evolution rules of LiMn₂O₄ with spinel structure in SIBs,but also provides a new strategy for recycling spent LIBs,to directly reuse spent electrode materials for next-generation batteries.?2?A high-performance Li_0.25Na_0.6MnO₂?LNMO?material is synthesized by solid-phase ball-milling method with the recycled LiMn₂O₄ as the raw material,and is used as cathode electrode material in SIBs to study its electrochemical properties and kinetic characteristics.Electrochemical test results show that LNMO has a high specific capacity and excellent rate performance.For example,when the current densities are 10,20,50,100,200 and 500 mA g^-1,the discharge specific capacities of LNMO are 131.5,126.3,117.7,110.1,103.7 and 92.9 mAh g^-1,respectively.When the current density returned to 10 mA g^-1,the discharge specific capacity is 128.8 mAh g^-1,which is 97.9% of the initial capacity,indicating that the extraction/insertion process of ion is reversible.In addition,the kinetic process of LNMO electrode is studied by cyclic voltammetry with different scanning rates,and the apparent ion diffusion coefficient of LNMO is calculated to be 1.26×10^-12cm² s^-1based on the test results.Thus,LNMO has an excellent kinetic characteristics.The proposal of this work provides ideas for the recycling and reuse of other spent LIBs.