The Electrochemical Performance Of Sn₄P₃-based Composite For Lithium Storage

Tin phosphite?Sn₄P₃?has low cost and high theoretical capacity.However,this material suffers a huge volume expansion during Li⁺intercalation/deintercalation process,which leads to rapid capacity decay.In this paper,planetary,ordinary vibrational and plasma assisted ball milling?P-milling?were adopted to improve the cycling performance of Sn₄P₃-based anode material by means of composite,nanocrystallization and amorphization.Sn₄P₃-AC anode material was prepared by combining Sn₄P₃ with amorphous activated carbon?AC?through planetary and ordinary vibrational ball milling.Under the action of vibrational ball milling,the grain size of Sn₄P₃ in the composite can be refined to 25-50nm.With the addition of carbonaceous material AC,the cyclic stability of the material can be effectively improved.Therefore,when the composite was used as anode for lithium ion batteries,the reversible capacity of 694.9mAh/g can be maintained after 250 cycles at a current density of 1A/g.The expanded graphite?EG?with layered structure was used as a carbon source to obtain Sn₄P₃@FLG nanocomposite by planetary and ordinary vibrational ball milling.Compared with AC,EG depends on its large layer spacing,which is easily exfoliated in the ball milling process to form few layered graphene?FLG?coated on the surface of Sn₄P₃ nanoparticles.And the two materials are closely connected by P-O-C bonds.This FLG coating structure can more effectively inhibit the volume expansion of Sn₄P₃ during the cycle.At a current density of 1A/g,the anode material can still maintain a reversible capacity of 929.6mAh/g after 830 cycles,with a capacity retention is up to 87.0%.In order to obtain a Sn₄P₃-based anode material with higher capacity,SnP₃ was prepared by increasing the molar ratio of P to Sn in the first planetary ball milling process.Sn₄P₃-P@FLG composite was synthesized via the second P-milling.The increase in P content can improve the lithium storage capacity of the material,while Sn₄P₃ has higher intrinsic conductivity and better cycling stability than SnP₃.Amorphzation can reduce the mechanical strain of the material during continuous lithium storage/release to maintain its structural integrity and provide more open diffusion channels for ion transport.Hence,the reversible capacities of this Sn₄P₃-P@FLG composite at 1A/g for the 1st and 425th cycles can reach 1224.1mAh/g and 1104.5mAh/g,respectively.