Effect Of Tungsten Doping On Structure And Electrochemical Properties Of Ni/co/mn-based Potassium Layered Cathode Materials

Potassium ion batteries（KIBs）have attracted wide attention as a possible alternative to lithium ion batteries（LIBs）for their similar electrochemical mechanism,low price and high natural potassium abundance.In this paper,three layered oxide cathode materials,namely,Co/Mn-based binary,Ni/Co/Mn-based ternary and tungsten-doped Ni/Co/Mn-based,were prepared by precipitation assisted solid phase method.The structure and electrochemical properties of these materials were studied emphatically.As the most promising cathode material for KIBs,the manganous-based layered oxide is inevitably caused by the Jahn-Teller effect caused by Mn³⁺/Mn²⁺,resulting in structural disorder,large size of K⁺ions and large volume change during the exfoliation/embedding process.Therefore,in this paper,Co doping was designed to reduce the structural transformation during depotassic process,and KCM-93-700 cathode material was synthesized.It has pure phase,high crystallinity,and lower content of Mn³⁺,providing up to 91m Ah g^-1 initial discharge specific capacity.At 0.5 A g^-1,the capacity remains40.9%after 500 cycles.Co element is expensive,rare and toxic,while Ni has the advantage of abundant reserves and low price.In order to further reduce cost and inhibit Jahn-Teller effect,this paper designed Ni-doped alternative Co and Mn,and synthesized Ni/Co/Mn-based ternary layered oxides.Under the influence of ternary synergistic effect,P2-K_0.66Ni_0.11Co_0.12Mn_0.77O₂（KNCM-7118-700）showed excellent rate performance,and the initial discharge specific capacity is 81.4 m Ah g^-1(current density is set to 50 m A g^-1).And in the high current500 m A g^-1,the discharge capacity of close to 30 m Ah g^-1 is still retained,but its cycle performance is poor.In addition to doping transition metals element and designing special morphology to improve the potassium storage performance of the positive electrode material,the non-electrochemically active element W is designed to be added in this paper.Due to the similarity between the ionic radius of W and TM,W occupies its vacancy and has more positive charge than K⁺.Therefore,W ion will show great attraction to the electrostatic charge of adjacent O-layer,thus inhibiting the collapse of the structure.P2-K_0.69Ni_0.10Co_0.11Mn_0.78W_0.01O₂（KNCM-W-2-700）has excellent performance ratio,At 10 m A g^-1,the capacity is up to 104 m Ah g^-1,and at 0.5A g^-1 the capacity remains 33m Ah g^-1.Moreover,in the cycle test at 0.5 A g^-1,the initial discharge specific capacity of up to 68 m Ah g^-1 was provided.After 1000 cycles,othe capacity still retained 45.9%.The assembled battery composed of KNCM-W-2-700//HC exhibits an energy density of 162.3Wh kg^-1,this design may provide valuable experience for advanced cathode materials for potassium ion batteries.