The Research On Application Of Natural Polymer Modified Binder To Silicon Anode Of Lithium Ion Battery

In the face of environmental and energy pressures,the world’s energy plate changes dramatically,and energy transformation has been unanimously recognized by all countries and regarded as the future direction.Under this circumstance,countries continue to increase the demand for batteries but also put forward higher requirements for battery energy density.At present,in the industry,the specific energy of the full-cell using graphite(based on the NCM cathode)as anode material is between 240-280 Wh.kg-1.If silicon is applied to the anode,the specific energy can be increased to 280-350 Wh.kg-1 or even higher.Therefore,silicon has excellent academic research and commercial application prospects in the field of anode materials.However,there are a series of problems such as volume expansion,electrode structure and conductive network failure in the process of battery cycle.As an important part of electrode structure,the binder can inhibit the volume change of silicon,so that the silicon anode can play a more excellent electrochemical performance.In view of the huge volume expansion of silicon anode and the poor stability of the electrode structure,this work uses polyacrylamide(PAM)to modify the soybean protein isolate(SPI)binder,enhancing the bonding ability and flexibility of SPI.Calcium ions(Ca2+)is used for modify the binder,giving the binder a certain rigidity in order to maintain excellent mechanical stability while restraining the volume expansion of silicon.Finally,this new kind of silicon anode binder with water soluble for lithium-ion batteries was made into electrode.The retention capacity of this electrode is 1248 mAh.g-1 after 300 cycles at 0.2 C(1 C=4200 mA.g-1)and at a constant capacity of 1000 mAh.g-1 the battery can stable cycle close to 450 times.When the silicon loading is 1.70 mg.cm-2,the electrode can maintain the capacity above 3.0 mAh.cm-2 for 90 cycles.In order to ensure the better bonding and mechanical properties of the binder,aiming at the failure of the conductive network,a kind of binder with three-dimensional cross-linked network structure(ST-PAM)was synthesized to achieve the network-plane contact with silicon particles and conductive additives,improving the stability of the electrode structure and maintaining the good electrical contact of the electrode.The binder take acrylamide(AM)as monomer,added amylopectin(ST)for grafting copolymerization,and introduce N,N’-methylene diacrylamide(MBAA)as crosslinking agent to form a cross-linking network.When it is applied to the silicon anode electrode,there is still 1944.86 mAh.g-1 capacity remaining after 100 cycles at 0.2C with 77.8%capacity retention rate,and the stable cycle is more than 200 cycles at 1500 mAh.g-1 constant volume charge-discharge test.It also can maintain capacity above 4.0 mAh.cm-2 for 60 times under high silicon loading(1.95 mg.cm-2).