Biomimetic And Surface Modification Of Lithium Ion Battery Anode Material

Lithium-ion batteries（LIBs）have been regarded as the prospective candidate for portable electronic devices,electric vehicles（EVs）and hybrid electric vehicles（HEVs）due to its high energy,no memory effect,low cost and long-term performance.With the environment and energy crisis occurring,LIBs have been the power source of the next generation of hybrid and pure electric vehicles,which have attracted significant attention in recent years.The increasing demands of high performance LIBs have motivated significant research in exploring low-cost and high-performance electrode materials.As we all know,anode materials are key ingredients of LIBs.Nowadays,the commercial LIBs anode materials graphite have disadvantages of low theoretical capacity(372 mAh g^-1)and fast capacity fading at higher current rates,which could not satisfy the increasing demands of the high performance of LIBs.Therefore,it is necessary to develop alternative anode materials with high theoretical capacity,good cycling and rate performance.ZnFe₂O₄ attract the most attention owing to its low cost and high theoretical capacity(1000.5 mAh g^-1).However,Zn Fe₂O₄ anode materials had the disadvantages of fast capacity fading and poor rate capability result from its low electronic conductivity and large volume expansion in lithiation-delithiation process,which restrain the widely application of this promising material.Many efforts have been done to conquer those disadvantages such as introducing conductive agents and constructing nanostructures,which do much better in improving the interface kinetic and electronic transmission capabilities and ensure their structural integrity and improves the cycling stability.Ti-based anode materials possess better cycle stability during the process of Li+ intercalation and deintercalation.The volume of the materials do not change and the materials have good cycle stability.Working voltage is about 1.5 V,which can effectively prevent the formation of metallic lithium dendrite and ensure the good safety performance during the charge/discharge process.Nevertheless,low electrical conductivity and flatulence of Li₄Ti₅O₁₂ limit the applications in Lithium ion batteries.At present,researchers will modify the material from introducing conductive agents and constructing nanostructures constructing nanostructures and surface coating.This work shortly introduced LIBs and critical materials,which focused on the modification methods of ZnFe₂O₄ and Li₄Ti₅O₁₂.Dopamine and its composites with many kinds of conductive agents were used to modify the surface of ZnFe₂O₄ and Li₄Ti₅O₁₂ via biomimetic method in the experiments.Finally,the composite materials were synthesized successfully,the following were the specific works:1.Nano ZnFe₂O₄ anode material was synthesized directly by simple and easy sol-gel method,polydopamine（PDA）was homogeneously coated on the surfaces of ZnFe₂O₄ particles by the self-polymerization of dopamine.The obtained ZnFe₂O₄/PDA electrode was protected and ionic conductivity was improved at the same time because PDA film was a good ionic permeable.The experiments optimized the thickness of coating layer by controlling the different reaction time.When the reaction time was 2 h,composites exhibited an initial discharge capacity of 2079 mAh g^-1 at 1 A g^-1,and obtained a reversible discharge capacity of 2074 mAh g^-1 after 150 cycles.Moreover,ZnFe₂O₄/PDA electrode showed a reversible discharge capacity of 1187 mAh g^-1 at 5 A g^-1.2.A double functional modified layer with ionic conduction and electronic conduction was developed,the modified layer contained polydopamine and different kinds of conductive agents.Dopamine had adhesion with any material,the appropriate amount of conductive carbon black was added to buffer solution of dopamine,the double functional modified on the surface of Zn Fe₂O₄ was achieved by the self-polymerization of dopamine.Based on the optimized coating thickness early,the different kinds of conductive carbon black（such as Super P and Graphene）were optimized and investigated the influence of different amount for ZnFe₂O₄ anode materials in the experiment.The results showed that ZFDASP2 composites displayed outstanding electrical performance when the content of Super P was 3%.The electrode showed a reversible discharge capacity of 2101.9 mA h g^-1 at 1 A g^-1 after 150 cycles.The ZFDAGO1 composites showed excellent electrical performance when the content of Graphene was 2%.3.The Li₄Ti₅O₁₂ anode material was modified via double functional coated layer,the conductive carbon black Super P was effective and the content of Super P was optimized.The LTOSP2 electrode showed an initial discharge capacity of 175 mA h g^-1 at 35 mA g^-1,but the unmodified Li₄Ti₅O₁₂（LTO）electrode showed an initial discharge capacity of 162.7 mA h g^-1 at 35 mA g^-1.The LTOSP2 electrode kept a higher discharge capacity after 150 cycles.