Preparation And Sodium Storage Properties Of Nickel Selenide Composite Materials

Nickel diselenide（NiSe₂）has many advantages such as easy to synthesis,high theoretical specific capacity,abundant reserves,and low price,which is an ideal anode material for sodium ion batteries.However,the internal volume expansion and slow kinetics of NiSe₂ leads to the low rate performance and cycle stability.To solve the above problems,the paper takes NiSe₂ as the research object,through introducing carbon materials,constructing heterostructures and constructing hollow structures to improve its electrical conductivity,rate performance and cycle performance,systematically study its microstructure and electrochemical behavior,and reveal the sodium storage performance and mechanism.The carbon composite spherical NiSe₂ electrode material was prepared,and the process parameters were optimized.NiSe₂ particles were evenly distributed on the carbon layer without agglomeration,and the particle size was smaller,which effectively improved the conductivity and sodium storage performance,the initial specific capacity is high,and the specific capacity at 0.1 A g^-1 current density is 469.5 mAh g^-1,close to the theoretical value of 494 mAh g^-1.In the process of preparing carbon composite NiSe₂,an oxidation step is added to prepare a carbon composite NiSe₂ heterostructure.By adjusting the oxidation time,the change of oxygen content affects the phase composition of the selenization product.When the oxidation time is 6 h,the carbon composite NiSe₂/Ni_0.85Se heterostructure is prepared,which effectively improves the cycle performance and rate performance of the material.The capacity retention rate is 89.4% after 50 cycles at a current density of 0.1 A g^-1;the specific capacity can reach 454.0 mAh g^-1 at a current density of 2.0 A g^-1.According to the principle of Ostwald ripening method,solvothermal method is adopted to prepare NiSe₂ with hollow nanosheet microsphere structure by adjusting the ratio of raw materials.The hollow structure significantly eased the volume expansion of the material and improved the cycle stability.The specific capacity after 50 cycles at a current density of 0.1 A g^-1 was 264.0 mAh g^-1,and the retention rate was close to 68.2%.