Investigation On Modified Starch Binder For Silicon Anodes Of Lithium-ion Batteries

Silicon(Si)is regarded as a promising anode maternal among many candidate materials due to its high theoretical specific capacity(4200 mAh/g),which is 10 times higher than that of commercial graphite material(370 mAh/g).However,the practical application of Si anode faces a huge challenge that they undergo repeated volume expansion(>300%)and contraction during cycling,resulting in a rapid decline in capacity.As an important part of electrodes,binders play the role of bonding active materials and the current collector,maintaining the structural integrity of electrodes during cycling.Therefore,the developmentment of new binders with high performance helps to improve the performance of Si anode lithium-ion batteries.The main work of this paper is as follows:1.Oxidized starch(OS)with different degrees of oxidation(1%,5%,10%,20%,40%)was prepared by hydrogen peroxide oxidation.The electrochemical performance of SiNPs anode with the different OS is conducted and compared.SiNPs/OS(40%)shows the best electrochemical performance.The SiNPs/OS(40%)electrodes exhibit capacity retention of 72.1%after 100 cycles at the current density of 0.4 A/g,and shows a discharge capacity of 1123 mAh/g at a high current density of 8 A/g.The better electrochemical performance of SiNPs/OS(40%)electrodes can be attributed to the more carboxyl group of OS(40%),which can effectively accommodate the volume change of Si anode after the reaction between the carboxyl groups and hydroxyl groups on the silicon surface.2.OS-CMC binder with 3D network structure is prepared by cross-linking oxidized starch(OS)and sodium carboxymethyl cellulose(CMC).OS-CMC shows better thermal stability,chemical stability,and mechanical properties.The SiNPs or SiMPs anode with OS-CMC binder exhibit the best electrochemical performance among OS,OS-CMC,and CMC binder.The capacity retention of SiNPs/OS-CMC and SiMPs/OS-CMC after 100 cycles is 73%and 57.35%at a current density of 0.4 A/g,respectively.SiNPs/OS-CMC shows a discharge capacity of 1667 mAh/g at a high current density of 1667 mAh/g.The 180° peeling test demonstrate that OS-CMC binder possesses stronger peeling strength than OS and CMC binder.The 3D network structure of OS-CMC binder can effectively accommodate the volume change of Si anode,avoiding the shedding of active materials and maintaining the integrity of electrodes.3.Starch-sodium alginate(ST-Alg/Ca2+)binder was designed and prepared.The SiNPs with ST-Alg/Ca2+binder exhibit better electrochemical performance than ST and Alg.SiNPs/(ST-Alg/Ca2+)show higher initial coulombic efficiency of 82.6%than that of SiNPs/ST and SiNPs/Alg at a current density of 0.4 A/g.Besides,the capacity retention of SiNPs/(ST-Alg/Ca2+)after 100 cycles is 72.4%,which is higher than 56.7%and 57.3%of SiNPs/ST and SiNPs/Alg.At a high current density of 8 A/g,SiNPs/(ST-Alg/Ca2+)also has a discharge capacity of 1202 mAh/g.The SiNPs/(ST-Alg/Ca2+)possess the highest lithium ion diffusion coefficient calculated by the CV method.The cross-linked structure of ST-Alg/Ca2+ binder is conducive to maintain the integrity of electrode during cycling,resulting in good electrochemical performance.