| The development of lithium-ion batteries(LIBs)in recent years has encountered bottlenecks due to the expensive and unevenly distributed lithium resources.Development in the post-LIBs era is expected to meet this challenge by reducing the use of decreasing lithium resources.Therefore,researchers have been hunting for a novel laboratory technique to deal with it.The redox potential of K+/K(-2.93 V)is closer to that of Li+/Li(-3.04 V).In terms of high voltage and energy density,potassium-ion batteries(PIBs),are expected to achieve the same advantages as LIBs.And K resources are cut-price compared with that of lithium,expecting to obtain output voltage and energy density comparable to LIBs at a lower cost.Moreover,compared to Li-ion(4.8 A)and Na-ion(4.6 A),K-ion has the smallest Stokes radius(3.6 A),with the highest ion mobility and conductivity in solution.Moreover,the diffusion coefficient of K-ion is about 3 times that of Li-ion.Based on the above advantages,PIBs are an effective alternative to LIBs.The slow reaction kinetics,nevertheless,caused the low first coulombic efficiency(ICE)and the damage caused by the large mechanical deformation of the electrode during the de-intercalation process due to the large K-ions(1.38 A),which makes the electrochemical performance of PIBs unsatisfactory.Transition metal phosphide(TMP)anode materials stand out among many reported anode electrode materials(including metal compound,alloy phase compounds,carbon materials,organic materials,etc.)due to high theoretical capacity and ionic/electronic conductivity,excellent thermal stability and ecological performance.Critical problems related,nevertheless,to large volume changes during the electrochemical cycle and slow reaction kinetics remain an insurmountable obstacle because of the large K-ions.There are also few reports on the reaction mechanism about TMPs.Moreover,the preparation methods of TMPs are mostly complicated and complicated.Therefore,appropriate strategies are used to construct structures,and rationally and deeply explore the mechanism of potassium ion storage reaction to solve the key problems that need to be conducted.Based on this work,a unique and simple preparation strategy is proposed to optimize the potassium storage performance of TMPs.In addition,the first principles and in situ test methods are combined to explore the K storage mechanism and reaction dynamics.The specific research work is conducted as follows:Herein,an integrated hybrid architecture composed of ultrathin CU3P nanoparticles(～20 nm)confined in porous carbon nanosheets(S-Cu3P?NPCSs)as a new anode material for PIBs is synthesized through a rational self-designed/template strategy.Benefiting from the unique structural advantages including more active heterointerfacial sites,intimate and stable electrical contact,effectively relieved volume change,and rapid K-ion migration,the S-Cu3P?NPCSs indicate excellent potassium-storage performance involving high reversible capacity,excellent rate capability,and superior cycling stability.Moreover,the strong adsorption of K-ions and fast potassium-ion reaction kinetics in S-Cu3P?NPCSs is verified by the theoretical calculation investigation.Noted,the intercalation mechanism of Cu3P to store potassium ions is,for the first time,clerly confirmed during the electrochemical process by a series of advanced characterization techniques.A type of anode material in which small-sized CoP nanoparticles coated with Ndoped carbon are immobilized into one-dimensional nitrogen-doped carbon matrix(CoP@NC?NCFs)that has been accurately synthesized via self-template catalysis.The hierarchical structure bears various structural advantages,including more active sites and ultra-high electrical conductivity provided by enriched nitrogen,strong interface interaction between CoP and N-doped carbon,the stability of the structure.As a result,the rapid potassium ion reaction kinetics and the strong adsorption of potassium ions of CoP have been realized,verified by galvanostatic intermittent titration technique(GITT)and density function theory(DFT)calculations.What’s more,through the advanced in-situ characterization techniques,the solid-solution reaction mechanism of CoP and potassium ions has been clarified.Zero-strain structure further makes sure the structural robustness and enables CoP@NC?NCFs demonstrate excellent potassium storage properties,especially,cycle stability with capacity of～206 mAh g-1 at 0.1 A g-1 for 1200 cycles,achieving an ultralow decay rate of 0.01%.The corresponding K-ion full cell is also prepared,as expected,and shows stable capacity retention.An elegant and novel type of anode material where FeP nanoparticles(about 50 nm)are embed into one-dimensional nitrogen-enriched porous carbon frameworks and there is hollow structure around them(FeP@void-NC?NPCFs),which has been ingeniously fabricated by self-template/catalysis method.The elegant structure bears multiple structural advantages,including more active sites and excellent conductivity provided by nitrogen enriched,strong interface effects(between FeP and N-doped carbon)supplied by the C-N and C-P bonds,as well as structural stability are included,which leads to FeP@void-NC?NPCFs with excellent K-ion electrochemical performance,especially,long-term cycling stability with capacity of about 248 mAh g-1 under 0.1 A g-1 over 1200 cycles,obtaining an ultra-low decline rate(0.001%).Moreover,the full cell of K-ion is also fabricated,sure enough,and demonstrates stable cycling capacity retention.In addition,a series of electrochemical analysis(including impedance,galvanostatic intermittent titration technique,and cycle measurement)and density function theory calculations verified its rapid potassium ion reaction kinetics and strong adsorption of potassium ions.Last but not least,the reaction mechanism of FeP and potassium ions has been clarified through the advanced in-situ characterization techniques. |
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