Surface Modification Of Nickel-rich Layered Cathode Materials For Lithium-ion Batteries

Lithium ion batteries are expected to be the next-generation energy-storage devices for renewable new energy,and will be widely used in electric vehicles,smart grids and other fields.However,the development of lithium ion batteries is limited by a lot of problems.In order to meet the the demand of new generation of electronic devices,lithium ion batteries should have high energy density,long cycle life and good thermal stability.LiNi_0.8Co_0.15Al_0.05O₂?NCA?has been considered to be one of the most attractive cathode candidates for rechargeable lithium batteries because of its high capacity and low cost.There are several challenges still remain to be solved such as poor cycling performance and thermal stability.This research is mainly foucused on the enhancement of the electrochemical performance of NCA by surface modification.The main research results are as follows:?1?We prepared a Co₃O₄-modified NCA cathode material with a facile wet-chemical route.The as-prepared Co₃O₄-coated NCA cathode material delivers a specific capacity of207.6 mA h g^–1 with an initial Coulombic efficiency of 90.8%at 0.1 C.The capacity retention of the Co₃O₄-coated NCA cathode material is as high as 91.6%at 1 C between the potential from 2.8 to 4.3 V after 100 cycles.More importantly,the capacity retention of the resulting Co₃O₄-coated NCA is higher than 94.7%after 100 cycles at 0.2 C.In addition,the Co₃O₄-coated NCA cathode material exhibits good rate capability,especially a high discharge capacity at a high current density,Co₃O₄-coated NCA delivers a specific capacity of 144.9 mA h g^–1 at 10 C.When the current density is back to 0.2 C,the discharge capacity is 204.1 mA h g^-1.The outstanding electrochemical performance of Co₃O₄-coated NCA is assigned to the surface coating layer can protect the cathode materials from electrolyte.In addition,Co₃O₄ may react with lithium-containing impurities to form Li_xCoO₂ on the surface and decrease the charge-transfer resistance.?2?We coated NCA with Sm-doped CeO₂ thorough a wet-chemical method to improve the cycling performance and rate capability.After surface modification,the coated material delivers a specific capacity of 175.5 mA h g^–1 at 1 C between the potential from 2.8 to 4.3 V,and the capacity rention is 97.0%after 100 cycles.It is believed that the better cycling perfoemance may benefit from the stability of NCA improved by Sm-doped CeO₂ coating layer.Also,it exhibits good rate capability,due to the decrease of the charge-transfer resistance.?3?The Atomic layer deposition?ALD?technique will obtain highly uniform coating layer with a well-controllable thickness compared with the traditional coating methods.In this work,we investigate the performance of NCA electrodes with an ALD TiO₂ layer for charging and discharging in the range from 2.8 to 4.3 V.TiO₂ has been investigated to modifify the cathode materials.We optimized the thickness of the coating layer to 4 nm,and the sample delieves 173.5 mA h g^-1 at 1 C.The capacity rentention is 97.4%after 100 cycles.The cycling performance is enhanced by the TiO₂ layer that will suppress the polarization of the electrode and improve the structural stability.