The Research On Phase Change And Metal Recycling In The Roasting Process Of LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O System

Under the call of the concept of sustainable development,the replacement of traditional fossil fuel vehicles by electric vehicles has gradually accelerated,which has greatly promoted the development of the power lithium-ion battery industry.At the same time,as a large number of power lithium-ion batteries enter the recycling system,improve the recycling system of scrapped power lithium-ion batteries,and implement the low-cost,green and efficient recycling of scrapped power-ion batteries,it is necessary to carry out technical basic research on the recycling of scrapped lithium-ion batteries.This thesis takes the recovery of the valuable metals Li,Ni,Co and Mn as the research object of LiNi_0.6Co_0.2Mn_0.2O₂as the cathode material of the end-of-life power lithium-ion battery,and study on the change rule and control mechanism of the metal elementoccurrenceformduringtheroastingprocessof LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O system,and the roasting-water immersion process is used to recover the metal,and the key factors that affect the metal recovery rate are studied.The research content includes the change characteristics of the occurrence form and ion valence of Li,Ni,Co and Mn in the acidic roasting environment,and reveals the distribution and distribution characteristics of the metal elements from the perspective of mechanism.The research results obtained are as follows:(1)The LiNi_0.6Co_0.2Mn_0.2O₂material exhibits thermodynamic stability during heating from room temperature to 600°C,while the mixture composed of LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O undergoes significant chemical conversion during the roasting process,it is characterized by the generation of new phases.When the mixing mass ratio of LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O in the roasting system is1:1.41,more than 90%of Li in the layered structure of LiNi_0.6Co_0.2Mn_0.2O₂is chemically converted to form a soluble Li sulfate,Li element is transferred to the water leaching solution in the form of Li⁺;under the same roasting conditions,Ni,Co,Mn elements and Li elements show greater differences,only less than 10%of Ni,Co,Mn elements exist in the leaching solution in the form of soluble Ni²⁺,Co²⁺,Mn²⁺in.The results show that Li element preferentially undergoes chemical conversion over Ni,Co,and Mn elements.As the form of occurrence of Li element changes,the layered structure of the cathode material LiNi_0.6Co_0.2Mn_0.2O₂is destroyed,and the morphology of the material changes from uniform particles to massive particles with different sizes,it increases after roasting and has a slight sintering phenomenon.The main elements contained in the roasted product are Na,S,O,Li,Ni,Co,Mn,and the occurrence form of Li element is Na Li SO₄.Mechanism studies have shown that controlling the amount of NaHSO₄·H₂O added in the system actually adjusts the partial pressure of SO₃produced by the thermal decomposition of NaHSO₄·H₂O during the roasting process,which can give priority to the Li element in the cathode material LiNi_0.6Co_0.2Mn_0.2O₂to achieve the purpose of step-by-step recovery of valuable metals.(2)In the roasting system,when the mixed mass ratio of LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O increases from 1:1.69 to 1:4.49,the change law of the respective occurrence forms of Ni,Co,and Mn elements is as follows:Ni:LiNi_0.6Co_0.2Mn_0.2O₂?Ni₆Mn O₈?Na₂Ni(SO₄)₂,Ni₆Mn O₈?Na₂Ni(SO₄)₂,Ni O?Na₂Ni(SO₄)₂,Na₆Ni(SO₄)₄;Co:Mn Co₂O₄?Co₃O₄?Co₃O₄,Na₆Co(SO₄)₄?Co O,Na₆Co(SO₄)₄?Na₆Co(SO₄)₄,Na₂Co(SO₄)₂;Mn:LiNi_0.6Co_0.2Mn_0.2O₂?Ni₆Mn O₈,Mn₃O₄,Mn Co₂O₄,Na₆Mn(SO₄)₄?Na₆Mn(SO₄)₄,Na₂Mn(SO₄)₂.When the mixing mass ratio of LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O roasting system reaches 1:4.49,the leaching rate of Li,Ni,Co,and Mn elements reaches 100%,indicating that in the roasting system of this composition,the elements Li,Ni,Co,and Mn are all converted into their respective metal sulfates.SEM-EDS results show that the microscopic morphology of the roasted product is massive particles with different sizes and irregular shapes,and the roasted product has a serious sintering phenomenon.The thermal decomposition product SO₃of NaHSO₄·H₂O makes the octahedral structure of Li-O and Me-O(Me=Ni,Co,Mn)unstable and collapses,which results in the chemical conversion of Li,Ni,Co and Mn elements from the positive electrode material LiNi_0.6Co_0.2Mn_0.2O₂with a layered structure of?-Na Fe O₂in a certain order to form metal sulfates.Based on the above research,the LiNi_0.6Co_0.2Mn_0.2O₂-NaHSO₄·H₂O system is used for roasting,and the roasted product is leached with water to transfer lithium,nickel,cobalt,etc.to the leaching solution.This process is feasible to recover metals.