Design Of Micro-nanostructured Based On Insertion-type Anode And Their Potassium Storage Mechanism Researches

Nowadays,rechargeable batteries play an irreplaceable role in powering the consumer electronics and large-scale energy storage device.Among these alternative candidates,potassium ions batteries?PIBs?have drawn growing attentions due to the low-cost and low standard potential of potassium,which can ensure the cost-effectiveness and high energy density of PIBs.However,the major technical challenges faced by PIBs are the serious volume change and sluggish reaction kinetics of host materials during the charge-discharge process caused by the large scale of K ions,which can lead to the rapid degradation of electrochemical properties and restrict the practical applications of PIBs.In this regard,exploring suitable host materials with ultrastable structure and fast K ions transmission rate is of vital significance.The electrode meterials with insertion mechanism are a wise choice for the application of PIBs duo to their superior structure stability and fast K ions diffusion rate.Nevertheless,further development of insertion-type electrode is limited by their lower specific capacity and worse electronic conductivity,resulting in inferior K ions storage capability and worse rate performance.According to the problems of PIBs mentioned above,the research object of this paper is to improve the specific capacity and rate ability of insertion-type electrode.Thus,a serious insertion-extraction type materials such as?carbonaceous materails and titanium/vanadium oxide?have been designed,prepared and applied as anode materials for PIBs.Their excellent K ions storage capability and mechanism are in-depthly studied and detailed discussed.The related results are listed below:Carbonaceous materials for potassium-ion batteries?PIBs?are quite attractive for the cost-effective feature.However,the cycle stability and rate performance of carbonaceous anode materials based on PIBs are limited.Thus,the nitrogen?N?and sulfur?S?codoped carbon microboxes?NSC?with increased interlayer spacing is prepared via a carbonization-etching process.Unlike the traditional graphite,in which the K ions are difficult to insert into the restricted interlayer spacing,the NSC displays extremely large interlayer spacing of 0.412 nm,making the K ions more flexible during the insertion/extraction process in NSC.Moreover,ex-situ TEM study reveals that the layer structure of NSC is well-remained during the potassiation/depotassiation process.As a result,the NSC delivers super-long cycle life(180.5m Ah g^–1 at 500 m A g^–1 after 1000 cycles)and extraordinary rate ability(155.6 m Ah g^–1 at 2 A g^–1),which makes the NSC a promising anode material for PIBs.In this work,high pyridine N-doped porous carbon synthesized at 600 ^oC?NPC-600?derived from the metal-organic frameworks?MOFs?has been fabricated and employed as the anode material for PIBs.NPC-600 can deliver a high reversible specific capacity(587.6 m Ah g^-1 at 50 m A g^-1),outstanding rate properties(186.2 m Ah g^–1 at 2 A g^–1)and cycling performance(231.6 m Ah g^–1 at 500 m A g^–1 after 2000 cycles).The excellent electrochemical performance could be attributed to the increased amounts of of pyridine N and neglectable change of interlayer space during potassiation/depotassiation process of NPC-600,which can provide additional adsorption sites to“capture”more K ions and ensure the structure stability.This work provide a new strategy to improve the electrochemical performance of carbonaceous anode for PIBs.In this work,hierarchical H-Ti O₂-C micro-tubes?MTs?composed of heterostructured Ti O₂-C nanosheets?NSs?have been fabricated through a facile wet-chemical method.H-Ti O₂-C MTs demonstrate an enhance K⁺accommodation capability,exhibit a high specific capacity(240.8m Ah g^–1 at 100 m A g^–1),exceptional rate capability(208.5,180.1,114.6 and 97.3 m Ah g^–1 at200,400,1000,and 2000 m A g^–1,respectively),good cycling stability(132.8 m A g^–1 at 500m A g^–1 after 1200 cycles).The Ti O₂/C heterointerface plays a vital role in achieving the excellent electrochemical performance by enhancing affinity between Ti O₂ and carbon,stabilizing Ti O₂ and reaction products,providing improved electronic and K⁺ions diffusion mobility.Here,guided by density functional theory?DFT?calculations,we demonstrate that the strategy of interfacial engineering via surface-amorphization of VO₂?B?nanorods?SA-VO₂?,which results in the formation of a crystalline core/amorphous shell heterostructure,enables superior K⁺storage performance in terms of large capacity,outstanding rate capability and long cycle stability working as an anode for PIBs.DFT calculations reveal that the created crystalline/amorphous heterointerface in SA-VO₂ can substantially lower the surface energy,narrow the band gap,and reduce the K⁺diffusion barrier of VO₂?B?.These conditions enable enhanced K⁺storage capacity and rapid K⁺/electron transfer,which result in large capacity and outstanding rate capability.Using in-situ X-ray diffraction and in-situ transmission electron microscopy complemented by ex-situ microscopic and spectroscopic techniques,we unveil that the superior cycling stability originates from the excellent phase reversibility with negligible strain response and robust mechanical behavior of SA-VO₂upon?de?potassiation.Overall,this work illustrates an efficient interfacial engineering strategy to enhance the energy storage performance of electrode materials for advanced PIBs.