Structure Design And Application Of Electrode Materials For High Performance Potassium Ion Batteries

Since the electrochemical energy storage technologies were raised,they have firmly occupied the majority of the energy storage market because of their high energy density and environmental friendliness.Lithium-ion batteries（LIBs）is a typical representative,which have been integrated into our daily life.However,lithium as a strategic resource is less abundant in the Earth’s crust and distributed regionally.Therefore,other metal-ion batteries（MIBs）with rich resource received more attention.Potassium ion batteries（PIBs）are considered to have great potential in large-scale energy storage applications because of their low redox potential and abundant resource.Compared with other metal-ion batteries,potassium has a lower standard electrode potential,which ensures their high energy density.In addition,the weak Lewis acidity of K⁺endows it a smaller solvation radius,leading to higher ionic conductivity and migration number.Particularly,K⁺can intercalate into graphite layers and form intercalated compounds,leading to a capacity of 279 m Ah g^-1,which provides their basis in large-scale application.However,the development of PIBs was still limited by the lack of advanced electrode materials.The traditional electrode material would suffer from serious volume expansion during repeated cycles due to the large radius of K⁺,which can cause huge damage to the electrode structure.Therefore,the design and construction of electrode materials capable of reversibly accommodating K⁺is the key to achieve the commercial application of PIBs.To this end,a variety of advanced cathode and anode materials were successfully constructed for PIBs with high energy density and power density.The main contents and innovations are as follows:A low-cost BR-rGO cathode material was successfully constructed for PIBs base on covalent bond and intercalation strategy.The intercalation reaction between BR molecules and rGO would expand rGO layers spacing,facilitating ion transport.In addition,BR molecules were anchored on the surface of rGO by the C-N covalent bond between BR and rGO,thus effectively inhibiting its dissolution in the electrolyte and greatly improving the utilization of active material.As a result,BR-rGO can exhibit a high capacity of 171 m Ah g^-1 and decent cycle stability.The full cell also achieves a high energy density of 168 Wh kg^-1 and long cycle life（over 3,000 cycles）.These results demonstrate the success of the structural design and validate the application potential of BR-rGO.A carbon fiber anode material（O-C600）with fast ion transport channels was successfully designed and constructed for high power density PIBs.The high carboxylic group content in fibers can not only provide more active sites,improving reversible capacity,but also increase its wettability in electrolyte.In addition,the abundant ion channels in the structure greatly shorten ion diffusion path,enhancing K⁺transport kinetics.As a result,O-C600 anode shown excellent rate capabilities and long cycle performance.Even at the extreme current density of 40 A g^-1,a high reversible capacity of 78 m Ah g^-1 can be achieved.The full cell also presented a superior power density of 23,750 W kg^-1,and completed a 61%charge capacity in 11seconds.A three-dimensional porous Bi-MOF anode material was designed and constructed.In Bi-MOF,Bi³⁺is coordinated with terephthalic acid to form a porous network structure.When applied as the anode for PIBs,Bi can alloy with K⁺,greatly improving the capacity,and the reduction product can increase the conductivity of electrode.Besides,the organic parts in Bi-MOF not only provides the adsorption site for K⁺,but also can well accommodate the volume expansion and ensure the integrity of the electrode structure.As a result,Bi-MOF anode can exhibit high reversible capacity of 419 m Ah g^-1 and excellent cycle performance.The energy density of 183Wh kg^-1 can also be achieved in full battery.Porous Ni Co_1.15S₄ nanopyramids wrapped in rGO(Ni Co_1.15S₄@rGO)were proposed as an advanced anode for PIBs.Based on the operando XRD results,the reaction mechanism of Ni Co_1.15S₄@rGO electrode was proved to be related to the insertion/extraction and phase conversion processes.We show that the cycling degradation of Ni Co_1.15S₄@rGO electrode is mainly due to the inferior reaction kinetics for the irreversible phase conversion.To optimize K⁺storage properties,we tune the potential window（0.25-2.5 V）of Ni Co_1.15S₄@rGO anode,which enables a high reversible capacity of 436 m Ah g^-1 at 0.5 A g^-1 and a stable cycling over 300cycles.Homogenous cobalt selenide embedded in hyperconjugated frameworks(Co Se_2-x-rGO)were designed and constructed for high-energy potassium ion batteries.This ultra-thin two-dimensional structure not only greatly expands the contact area between electrode and electrolyte,providing more reactive site,but also improves the conductivity of electrode.In addition,the presence of homogeneous junction interfaces and abundant Se vacancies in the structure can induce the generation of tiny region electric field,which can greatly accelerate ion/electron transport.Thus,the Co Se_2-x-rGO anode can achieve ultrahigh reversible capacity of 639 m Ah g^-1 at0.1 A g^-1,extraordinary rate capability of 169 m Ah g^-1 at 10 A g^-1,as well as outstanding cyclability(312 mA h g^-1 after 1000 cycle at 2 Ag^-1).