Study On Preparation, Structure And Electrochemical Performance Of Phenolic Resin-based Hard Carbon Anode

Anode materials are an important part of lithium-ion batteries.At present,graphite is the most common anode material.However,the limited theoretical capacity and rate performance of graphite limits the continued development and application of lithium-ion batteries.It is urgent to seek alternative anode materials with high capacity and great rate performance,and hard carbon is an excellent candiate.This paper focuses on the application of phenolic resin-based hard carbon in lithium-ion batteries,including the following three parts:?1?Hard carbon was obtained from Novolak-type phenolic resin and Resole-type phenolic resin with different molecular weight by vacuum carbonization at 800?.The results show that the molecular weight of phenolic resin significantly affect the interlayer spacing and the degree of disorder,and further affect the electrochemical properties of hard carbon.The effect of molecular weight on the structure of different phenolic resins is opposite.For Novolak-type,the increase of molecular weight leads to the increase of interlayer spacing and disorder;for Resole phenolic resins,the law is opposite.The structure of low molecular weight phenolic resins is more conducive to lithium storage,which leads to the improvement of electrochemical performance.Among them,the low molecular weight Resole-type hard carbon has the largest d₀₀₂?3.76??and ID/IG?2.7?,so that it has the highest reversible capacity,rate performance and the first coulomb efficiency,the first charge capacity is 606 mAh g^-1 at the current density of 50 mAg^-1 and the reversible capacity at the current density of 100,200,300,500 and 1000 mAg^-1 is 450,360,340,300 and 270 mAh^-1,respectively.?2?The effects of different solvents?methanol,ethanol,ethylene glycol,propanol,propylene glycol?on the morphology,pore structure and electrochemical properties of hard carbon were studied.For Novolak-type,monohydric alcohol has little effect on morphology,structure and electrochemical properties.With propylene glycol as solvent,the specific surface area and number of mesopores increased,leads to best electrochemical performanc.The first reversible capacity is 507 mAh.g^-1,and the capacity retention rate is 73.2%after 40 cycles,respectively.The average reversible capacities at current densities of 50 mA^-1,100 mA g^-1,200 mA g^-1,300 mA g^-1,500mA g^-1 and 1000 mA g^-1 are 460 mA h g^-1,360 mA h g^-1,320 mA h g^-1,300 mA h g^-1,280 mA h g^-1 and 250 mA h^-1,respectively.?3?For Resole-type,solvent types not only affect the microcrystalline structure and pore structure,but also affect the morphology of hard carbon.Using diol?ethylene glycol,propylene glycol?as solvent,hard carbon will become cluster structure with increased interlayer spacing,specific surface area and the mesoporous,and its capacity and rate performance will be improved.When propylene glycol was used as solvent,the hard carbon obtained the highest specific capacity and best rate performance.The first reversible capacity was 665 mAh g^-1,and the capacity retention rate after 30 cycles was 73.9%,respectively.The average reversible capacities at the current density of 50mAg^-1,100 mAg^-1,200 mAg^-1,300 mAg^-1,500 mA g^-1 and 1000 mA g^-11 were 620 mAh g^-1,490 mA h g^-1,420 mA h g^-1,390 mA h g^-1,370 mA h g^-1,330 mA h g^-1,respectively.?4?Microcrystalline graphite/hard carbon?MG/HC?composite anode material was prepared by solid-liquid blending-carbonization method.The effects of the addition of microcrystalline graphite on the structure and electrochemical properties of the composite anode material were investigated.The results show that the structure of the composite anode material is hard carbon coated microcrystalline graphite particles.The thickness of HC decreases with the increase of microcrystalline graphite.The induced escaping effect of microcrystalline graphite can greatly reduce the formation of micro-holes?less than 1?m?in the composite anode material.Compared with pure phenolic resin-based hard carbon,the cyclic stability is significantly improved,but the specific capacity and rate performance of composite anode material will be reduced by adding excessive microcrystalline graphite.When the content of microcrystalline graphite is20 wt%of phenolic resin,the first charge capacity of composite negative material is477 mA h g^-1 at 50 mA g^-1 current density.After 100 cycles,the capacity of composite negative material is still 370 mA h g^-1,leading the retention rate of 79%,which is much higher than that of phenolic resin-based hard carbon after 100 cycles?59.2%?.When the current density is 1A g^-1,the capacity is 320 mA h g^-1,showing excellent rate performance.