Synthesis and Properties of Organic Quinone Electrode Materials for Alkali Metal(Li/Na/K) Ion Batteries

Author:Chen Lei

Supervisor:zhao yan ming


Degree Year:2019





In recent years,global warming and environmental pollution have became worldwide challenges,which motivate people to constantly explore more efficient clean energy.Among these,lithium-ion batteries(LIBs)are one of the green and effective energy storage technologies.However,the increasing demand of electric vehicles and large-scale energy storage systems makes it difficult for lithium-ion batteries to breakthrough due to thier cost,safety,energy density,and charge and discharge performance.Compared with traditional electrode materials,organic electrode materials have the advantages of high specific capacity,wide abundance,low cost(mainly consist of C,H,O,N,etc.)and sustainability.Moreover,the mechanical strength of organic materials are generally more flexible than that of inorganic materials,which is conducived to develop the stretchable batteries.Nevertheless,its practical application is still restricted by the following two aspects:one is the high solubility of organic materials,which could cause the serious capacity decay;the other is the inherent insulation,which could make poor rate performance.In this paper,we prepared several organic small molecules to design and optimize the electrochemical properties.Finally,the high-capacity,high-rate performance electrode materials would be received.The specific contents include the following parts:First,2,3-dichloro-5,6-dicyanoquinone(DDQ)is a common steroidal small molecule with potential sodium storage properties.However,high solubility and low electrical conductivity severely limit its electrochemical performance.In order to solve this issue,we optimize the content of conductive carbon black additive(Super P)during the electrode preparation process,which could not only inhibit the dissolution of active materials effectively,but also improve the electronic conductivity.The experimental results show that when the mass ratio of DDQ:Super P:PVDF is 30wt%:60wt%:10wt%,the DDQ composites,tested as anode electrodes for sodium ion batteries(SIBs),exhibit high capacity and good rate performance.In addition,the ex-situ SEM visually shows the change morphology changes of DDQ composites under different potential states.Finally,ex-situ FT-IR determined that the sodium storage mechanism of DDQ is related to carbonyl groups.Second,inspired by the first part of the work,DDQ composites also show good electrochemical performance when evaluated as anode electrodes for lithium-ion batteries(LIBs).Furthermore,we alter the functional group of DDQ.After hydrolysis,one of the cyano groups(-CN)in DDQ will be substituted by the hydroxyl group(-OH)to obtain 2,3-dichloro-5-hydroxy-6-cyano-1,4-benzoquinone(DHCQ).In this section,we tested DHCQ for the first time as anode electrodes for LIBs.The results show that under the same conditions,the DHCQ composites have higher specific capacity and rate performance than DDQ.This result may be related to the existence of hydroxyl groups could enhance the intermolecular interactions and suppress the dissolution of active materials in the electrolyte.Thirdly,we prepared the novel dihydroxybenzoquinone o-sodium salt(o-Na2C6H2O6)via a facile and effective method using the inositol(C6H6O6)and sodium carbonate(Na2CO3)as raw materials.And the as-prepared dihydroxybenzoquinone o-sodium salt(o-Na2C6H2O6)was evaluated as an organic electrode for lithium-ion,sodium-ion and potassium-ion batteries for the first time.The experimental results show that when o-Na2C6H2O6 is tested as the electrode material of LIBs,the first charge and discharge specific capacities are 200 mA h g-1 and 345mA h g-1,respectively.After 100 cycles,the charge specific capacity remains at 140 mA h g-1.In the rate test,the o-Na2C6H2O6 electrode still delivers a capacity of 55 mA h g-1 even at a current density of as high as 5 A g-1.On the other hand,in the sodium-ion half-cell test,o-Na2C6H2O6 exhibited an initial charge specific capacity of 168.1 mA h g-1,and the excellent rate performance(72.1 mA h g-1 at 5 A g-1-rate).Finally,when evaluated as elelctrode for PIBs,o-Na2C6H2O6 also has a first charge specific capacity of 168.1 mA h g-1 with coulombic efficiency of 77.4%,and a good rate performance(26.7 mA h g-1 at 5 A g-1-rate).These results are mainly attributed to the fact that the salinization could inhibit its solubility,resulting in the improvement of electrochemical performance.Hence,we think this work presented here also provides an important thought on other organic materials for rechargeable batteries.Then,based on the above studies,we have attempted to prepare electrode materials with different salinization sites through a simple synthetic way.The dihydroxybenzoquinone p-sodium salt(p-Na2C6H2O6)was synthesized in one step using a 30%solution of glyoxal(C2H2O2),sodium sulfite(Na2SO3)and sodium hydrogencarbonate(NaHCO3)as the raw materials.Benefiting from salinization,p-Na2C6H2O6 exhibits superior electrochemical performance as electrode materials for sodium-ion and potassium-ion batteries.Moreover,compared with o-Na2C6H2O6,p-Na2C6H2O6 exhibited higher specific capacity and rate performance.This result not only proves that the metal cation organic salt material can improve the electrochemical performance,but also indicates the different substitution position on organic structure could influence the electrochemical performance.Finally,as for inorganic materials,carbon coating and particle nanocrystallization are the two main ways to improve their electrochemical performance.In this part,we presented a simple synthetic method to constrain the Na3V2(PO4)3@C in hard carbon(the source obtained from pyrolytic polyaniline)(denoted as NVP@C@HC)to improve the electrochemical properties.Compared to the single carbon coating,this double-carbon-coated sodium vanadium phosphate has a high specific capacity of 111.6 mA h g-1 for 200 cycles at a current density of1 C,and maintains capacity retention of 95.3%.For rate performance,there is also a capacity of 61.0 mA h g-1 at 50 C.In the long cycle performance test,the NVP@C@HC composite could performs a long-term cycling capacity of 58.5 mA h g-1 exceeding 15 000 cycles at 20 C.The double carbon-coating not only improves the conductivity of the material,but also inhibits the growth of the particles and achieves fast diffusion of sodium ions.Therefore,we consider that the simple and cost-effective method would be helpful to extend to other carbon-coated composite materials,which needs increases in electronic conductivity.