Design,Synthesis And Properties Of Organic Anode Materials For Potassium Ion Batteries

Under the global carbon neutral and emission peak development concept,lithium-ion batteries,as a green energy storage device,have received extensive attention from the society.However,due to the lack of lithium mineral resources,uneven distribution and high cost,the application of lithium-ion batteries in the field of large-scale energy storage in China is significantly limited.In order to develop a new generation of low-cost energy storage devices,organic potassium-ion batteries have attracted the attention of researchers.When storing potassium ions,conventional inorganic materials have the common problems of structural collapse and poor stability.Compared with conventional inorganic materials,organic materials have been proved to be able to stably store potassium ions with larger ionic radius,and have the advantages of green environmental protection,designable structure and adjustable performance.However,in the existing reports,there is still a lack of organic electrode materials with excellent comprehensive properties,and their two serious problems generally faced are easy solubility and poor conductivity.In addition,during the charging and discharging process,active metal dendrites will be generated on the anode side of the battery,which affects the safety of the battery.In order to solve the above problems,several electrochemically active organic compounds are developed as anode materials for potassium ion batteries.The research focuses on organic molecular structure design,modification methods,electrochemical performance and energy storage mechanism to improve the energy density and cycle stability of organic electrode materials in potassium ion batteries,and promote the practical application of organic potassium ion batteries.The main research contents are as follows:(1)Using a simple and insoluble organic acid--Terephthalic Acid(H₂TP)as the anode active material,its lithium and potassium ion storage capacity is investigated.Cyclic tests and calculations show that H₂TP can generate H₂ and the corresponding terephthalate during the first reduction.After ball milling modification with conductive carbon black(Super P,SP),as an organic anode for Li-ion batteries,H₂TP can provide a high specific capacity of about 235 mAh·g^-1 at a high current density of 500 mA·g^-1with stable 500 cycles;as an organic anode for potassium-ion batteries,H₂TP exhibits an actual specific capacity of about 240 mAh·g^-1 and is capable of stable charge-discharge cycles for 150 times.The results show that H₂TP has the universal ability to store lithium ions and potassium ions,and can be used as organic anode materials for various alkali metal ion batteries.(2)In order to solve the solubility problem of organic small molecules in liquid electrolytes,“installing”ionic bonds on the structure of organic small molecules effectively solves the problem of organic electrode materials dissolved in electrolytes.Through the hydrolysis reaction,an organic compound--Potassium Perylene-3,4,9,10-Tetracarboxylate(K₄PTC)with four K-O ionic bonds is designed and synthesized.Cyclic Voltammetry(CV)tests and quantum calculations show that as a novel anode material for organic potassium ion batteries,K₄PTC exhibits two-electron redox activity with a theoretical specific capacity of 93 mAh·g^-1.After in situ recombination with Carbon Nanotubes(CNT),K₄PTC can achieve stable 2500 cycles at a high current density of 500 mA·g^-1,maintaining a highly stable practical specific capacity of 50mAh·g^-1.The results confirm that K₄PTC can achieve excellent cycling stability as an anode material for organic potassium ion batteries.(3)On the basis of the conclusion that K₄PTC has the ability to reduce solubility and improve cycle stability,in order to further achieve high specific capacity and energy density,a novel organic small molecule--1,4-Bis(1,4-Potassium Dicarboxylate Phenyl)Benzene(BBK₂TP)is designed and synthesized,and its electrochemical mechanism and charge-discharge performance for storing potassium ions is studied.BBK₂TP is successfully synthesized through a four-step reaction process,showing poor solubility in common electrolyte solvents.CV and charge-discharge tests find that BBK₂TP possesses 4-electron redox activity and can achieve a high theoretical specific capacity of 192 mAh·g^-1.During·cycling,BBK₂TP achieves stable 50 cycles and a practical specific capacity of up to 234 mAh·g^-1.As an anode material for potassium ion batteries,its median discharge voltage is 0.47 V.The results show that BBK₂TP can not only achieve high energy density in the full cell,but also avoid the formation of potassium dendrites,effectively improving the safety of the battery.(4)In order to promote the practical application of potassium-ion batteries,it is necessary to further study the electrochemical properties of organic potassium-ion full batteries with high working voltage.Using"potassium-deficient"Potassium Terephthalate(K₂TP)as the organic anode material and"potassium-rich"Poly(N-vinylcarbazole)(PVK)as the organic cathode material to prepare high-operating voltage(>2 V)and long-lifespan organic potassium-ion full cells(K₂TP//PVK).After material modification and electrolyte optimization,compared to the reported potassium-ion batteries based on organic anodes and organic cathodes,the K₂TP//PVK full cell exhibits a very high average operating voltage of 3.2 V and a minimum operating voltage of 2 V.At a high current density of 2 A·g^-1,K₂TP//PVK achieves 3000 charge-discharge cycles with an average discharge specific capacity of 46 mAh·g^-1.The results demonstrate that potassium-ion batteries using full organic electrodes can achieve high operating voltage and long·cycle lifespan.(5)In order to study the cycling stability of organic electrode materials in potassium-ion batteries,three insoluble organic compounds(small-molecule Bis(9,10-Anthraquinone)Benzene(BAQB),polymer--Poly(3,4,9,10-Perylene-Tetracarboxylic Acid Amide-1,4-Diaminoanthraquinone)(PPAQ)and Poly(1,4,5,8-Naphthalenetetracarboxylic Acid Amide-1,4-Diaminoanthraquinone)(PNAQ))are designed and synthesized,and their potassium-ion storage mechanism and charge-discharge performance also is studied.Solubility and charge-discharge tests find that the linear organic small molecule BAQB has excellent insolubility in common liquid electrolytes,showing an actual specific capacity of up to 232 mAh·g^-1(the Coulombic Efficiency is close to 100%).After 30 cycles,the capacity retention rate of BAQB is57%.The polymers PPAQ and PNAQ have better cycling stability.PPAQ achieves a stable 200 cycles with a capacity retention rate of 82.5%;PNAQ achieves a stable 200cycles at a current density of 100 mA·g^-1 with a capacity retention of 138 mAh·g^-1 and a retention rate of 92%.The results show that the polymer can achieve more stable charge-discharge cycles in organic potassium-ion batteries.