Construction,Lithium Storage Properties And Mechanism Of Sb-Pinning Lithium-rich Manganese-based Cathode Materials

Lithium-ion batteries have been widely used in portable electronic products,electric vehicles,power grid energy storage equipment and other fields due to their high energy density,no memory effect,environmental protection,safety and other advantages.As the core of lithium-ion batteries,the application of lithium-ion batteries cathodes such as cobalt-based（Li Co O₂）,nickel-based(Li Ni_0.8Co_0.1Mn_0.1O₂)and lithium iron phosphate（Li Fe PO₄）developed earlier is limited due to many factors such as resources,cost,energy density and stability.Lithium-rich manganese base transition metal oxides(Li_1.2Ni_0.2Mn_0.6O₂,LNMO)can trigger both oxygen anion and transition metal cation redox behavior,so the energy density can reach a higher level.However,in the high-voltage charging state,the irreversible migration of transition metal Mn ions and the oxygen release caused by O anion peroxidation will destroy the layered structure of material,resulting in voltage decay and capacity reduction.In view of these key scientific problems affecting the electrochemical properties of LNMO,this work successfully constructs a stable,high-capacity cobalt-free lithium-rich manganese-based cathode material Li_1.2Ni_0.198Mn_0.6Sb_0.002O₂（SLNMO）with non-transition metal element Sb pinned in the LNMO transition metal layer through structural modification.Compared with the original LNMO,SLNMO has a high capacity and energy density as well as stable electrochemical cycling performance and resistance to voltage attenuation.The main research contents are as follows:Aiming at the key problems of LNMO cathode materials,this study successfully constructed a stable high-capacity cobalt-free lithium-rich manganese-based cathode material Li_1.2Ni_0.198Mn_0.6Sb_0.002O₂（SLNMO）with non-transition metal element Sb pinned to the LNMO transition metal layers through structural modification.Compared with the original LNMO sample,SLNMO has high capacity and energy density as well as stable electrochemical cycling performance and resistance to voltage decay.Below are the main research highlights of this work:（1）In this work,a simple"sol-gel"and high-temperature sintering method were used to prepare the target product LNMO with good dispersion.Then,based on the preparation method of the pristine sample,the physical properties of Sb were innovatively used to successfully synthesize SLNMO with a good honeycomb ordered layer structure that was pinned to the LNMO transition metal layers.（2）Compared with LNMO,SLNMO has higher charge-discharge specific capacity,rate performance,and excellent electrochemical long cycling stability.SLNMO has a first-cycle discharge specific capacity of 301 m Ah g^-1 at a current density of 0.1 C and a high energy density of 1019.6 Wh kg^-1.After 200 cycles at 1C,the discharge specific capacity is retained by 181.8 m Ah g^-1,with a capacity retention of 86.03%.After a long electrochemical cycling,the discharge voltage decay of SLNMO is reduced 420 m V compared with LNMO.（3）The structural and chemical environment changes of the material were characterized by STEM,high-magnification ex-situ XRD,in-situ XRD,DEMS,XPS and other test technologies.It is proved that Sb effectively regulates anionic interaction and inhibits the irreversible migration of Mn³⁺.The reversibility of anionic redox to 2O^2-/O₂^n-has been improved,and the coordination environment of Mn O6octahedron is more complete,resulting in excellent cycle stability.（4）Through DFT theoretical calculations,confirming that Sb pinned in the LNMO transition metal layers,which effectively changes the Gibbs energy of Mn ions at different sites,and the density of states（DOS）level of Mn 3d and O 2p orbitals is also reduced to varying degrees.It’s proclaiming that SLNMO has a more thermodynamically stable Mn O6 octahedral field,prevents voltage decay and layered to spinel phase transition,increases charge transfer gap（Δct）for promoting reversible anion redox and reduces the formation of molecular oxygen.