Lithium-replenishing additive and preparing method thereof, and lithium secondary battery

A lithium secondary battery, comprising:

• a cathode sheet;
• an anode sheet;
• a separator;
• and
• an electrolytic solution, wherein
• the cathode sheet comprises a lithium-replenishing additive comprising:
• a lithium-rich-material core;
• and
• a shell layer disposed on the lithium-rich-material core, wherein
• the lithium-rich-material core is made of a lithium-rich material with an average chemical formula of aNixMyOz·bLi2O, wherein 0.95≤x≤1, 0.01≤y≤0.05, 1≤z≤1.15, 0.8≤a≤1.1, 0.8≤b≤1.1, and the M comprises one or more of copper (Cu), cobalt (Co), aluminum (Al), titanium (Ti), vanadium (V), zirconium (Zr), or iron (Fe);
• the shell layer comprises a polymer layer;
• and
• the shell layer further comprises an electrochemically active layer disposed on an outer surface of the polymer layer, and the electrochemically active layer is made of an electrochemically active material;
• and the electrochemically active material comprises one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate (LVP), lithium vanadyl phosphate, lithium vanadium fluorophosphate, lithium titanate, or lithium nickel cobalt manganate, wherein a mass of the polymer layer accounts for 1%-10% of a total mass of the lithium-replenishing additive.