Study On Preparation And Modification Of Nickel-rich Cathode Material For Lithium-ion Battery

Ni-rich cathode materials are widely used in new energy vehicles due to their high energy density and low price.However,because of the irreversible Li⁺/Ni²⁺disordering during the synthesis,and the instability of Ni⁴⁺ions within the deep delithiation,it is easy to cause the structural degradation from layered phase to unfavorable spinel and rock-salt phase,which eventually leads to poor cycling performance,rate capability and battery safety.In this dissertation,the effective strategies were applied to improve the electrochemistry performances of Ni-rich cathode material.The main works are as follow:?1?Aiming at the cation disordering in material and the poor stability of electrode-electrolyte interface,a heterogeneous structure is formed by spontaneous redox reaction between precursor and KMn O₄in an alkaline solution and subsequent calcination,which has high-capacity Ni-rich layered phase core and stable Li Ni_0.5Mn_1.5O₄-like spinel phase shell.Because the shell has similar and more robust cubic close-packed crystal structure and efficient 3D Li⁺diffusion channel,it can be in-situ formed on the particle surface,effectively inhibiting the surface phase transition and facilitating the Li⁺ions kinetics during cycling.The results show that the capacity retention at high cut-off voltage of 4.5V can still increase 11%at 1 C(200 m A g^-1)after 100 cycles,and the discharge capacity is as high as 153.7 m Ah g^-1at 10 C.?2?To improve the structure stability and thermal stability of material,tellurium?Te?doping in the Ni-rich layered oxide surface(Li Ni_0.88Co_0.09Al_0.03O₂)is proposed.It is confirmed that the doped Te⁶⁺is located in transition metal?TM?layer near the oxide surface,and its strong Te-O bond(548 k J mol^-1)can constrain the TM-O plane to further suppress the release of oxygen.Meanwhile,the reversibility of H2-H3phase transition is also improved to relieve effectively capacity decline and structural transformation at extended cycling.Therein,1 wt%Te doping?Te 1%-NCA?has the best improvement effect,and Te 1%-NCA cathode exhibits the improved cycling stability even at high voltages?4.5 V and 4.7 V?,and high thermal stability?the peak temperature of 258??.?3?For low Li⁺diffusion and structural degradation during cycling,a one-step dual modified strategy is proposed through wet chemistry method.Therein,a good ionic conductor YPO₄coating can suppress the electrode-electrolyte interface erosion reaction,while strong Y-O bonds can bind the TM-O plane to improve the stability of crystal structure during the deep delithiation?>4.3V?.Furthermore,the internal stress generated by the lattice anisotropy is effectively dissipated,thereby ensuring the high-capacity output and rapid Li⁺diffusion kinetics.The results show that the dual-modified Ni-rich cathode retains 94.1%capacity after 100 cycles at 1 C,and the discharge capacity can reach 159.7 m Ah g^-1at a large rate of 10 C.