| Under the dual carbon policy,new energy vehicles are the future direction of development,and the demand for power batteries is increasing,and its related mileage problems have become the focus of researchers.Currently,the gram capacity of high-end graphite anode has reached 360-365 m Ah/g,which is close to the theoretical gram capacity of 372 m Ah/g.Therefore,from the perspective of anode materials,it is necessary to develop new anode materials with higher gram capacity.Based on this,silicon-based materials with extremely high theoretical specific capacity have become the key research objects.However,the capacity decay caused by the huge volume expansion effect of silicon anode hinders its industrialization process.Aiming at the capacity failure mechanism of silicon,this paper provides countermeasures from the perspective of binder modification,which effectively alleviates the capacity decay problem of silicon-based lithium-ion batteries.Moreover,in order to reduce costs,the research in this paper is based on micron silicon,and the specific contents are as follows:(1)Boric acid(BA)and carboxymethylcellulose(CMC)are dissolved in water,and under the dual action of heating and stirring in a water bath,the B-O on the BA structure reacts with the hydroxyl group on the CMC,and a large number of hydrogen bonds generated can realize the construction of the electrode crossnetworked structure.Using pure silicon materials as active substances,the effects of binder products prepared by different crosslinking reaction temperatures and reactant ratios on the electrochemical properties are discussed.The results show that the BACMC-1:1-50°C binder prepared by the reaction of BA and CMC at a 1:1 mass ratio at50°C makes the pure silicon electrode obtain the highest reversible capacity(3269.80 m Ah/g)and initial coulomb efficiency(85.78%),which is much stronger than the traditional CMC binder system(the first circle reversible capacity is 2550.10 m Ah/g,and the initial coulomb efficiency is only 72.08%).For silicon-carbon electrode system,BA modified binder can also play a good effect,BA-CMC-1.5:1-50°C group with the best comprehensive performance,the reversible capacity of the first turn is1968.3 m Ah/g,the initial coulomb efficiency is 92.22%,after 100 cycles,the reversible capacity is still 1108 m Ah/g,the reversible capacity of the first turn of the traditional CMC group is 1864.6 m Ah/g,the initial coulomb efficiency is 91.96%,and after 100 cycles,the reversible capacity is only 725.75 m Ah/g;The peel strength test and scanning electron microscopy show that the peeling strength of the modified binder electrode piece is greatly improved,which effectively inhibits the volume expansion effect of the silicon-based electrode and maintains the integrity of the electrode.(2)The citric acid(CA)molecule has three carboxyl groups and one hydroxyl functional group on the C chain,and also has multiple active sites for hydrogen crosslinking with hydroxyl groups on the CMC chain.In this chapter,CMC is modified by CA,and under the condition of stirring in a water bath at 50°C,three groups of modified binders are prepared by the mass ratio reaction of CA and CMC at1:2,1:1 and 1.5:1,and applied to the micron silicon/carbon electrode system,which are recorded as CA-CMC-1:2-50°C,CA-CMC-1:1-50°C,CA-CMC-1.5:1-50°C,respectively.In comparison,CA-CMC-1:1-50°C binder has the best comprehensive performance: the peel test show the largest average peel force(0.23 N),which is more than three times the average peel force size(0.07 N)in the pure CMC group.The performance of electrochemical cycle is particularly prominent,after 100 cycles,the reversible capacity is still 1317.32 m Ah/g,and after 100 cycles of pure CMC,the reversible capacity is only 725.75 m Ah/g.The rate performance is excellent,and the reversible capacity of 1050-1100 m Ah/g can still be maintained at 1 C rate,and the capacity of the pure CMC group is almost 0.Good maintenance of integrity between electrode components and low electrochemical impedance.(3)The optimal bonding group obtained in parts(1)and(2)was applied to the pouch battery with a design capacity of 1350 m Ah,and the capacity retention rates of BA-CMC-1.5:1-50°C and CA-CMC-1:1-50°C are 78.3% and 78.61% after 400 cycles under the charge/discharge test conditions of 0.5 C/1 C,while the capacity retention rate of the traditional CMC binder pouch battery only 69.56% after 400 cycles.The SEM test results show that after 200 cycles,the surface of the CMC electrode is extremely uneven,obvious cracks can be observed,and there is a tendency of pulverization,the cross-section is thickened by 39.5 μm,the expansion rate reaches 40.7%,and the electrode material and the foil are detached,while the surface of the BA-CMC-1.5:1-50°C and CA-CMC-1:1-50°C electrode has no cracks,the cross-section is thickened by 9.5 μm and 16 μm,and the expansion rate is 9.8%and 16%,respectively.The results show that both BA and CA-modified CMC binders can effectively improve the electrochemical performance of silicon anodes. |
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