| Due to its extremely high theoretical specific capacity(4200 m Ah g-1),silicon（Si）based anode are expected to replace graphite electrodes(theoretical specific capacity372 m Ah g-1)as new high-capacity lithium-ion battery anode,and are considered to be the most promising lithium-ion anode material for the next generation.However,the huge volume expansion（>300%）caused by Si-based anode during battery cycling can lead to electrode structure damage,electrical contact failure,and other side reactions.Eventually,it leads to rapid degradation of battery capacity and poor cycle stability.To solve the above problems,researchers have attempted to conduct a large number of experimental attempts by preparing nano Si materials and composite Si materials,developing new electrolyte additives,and new adhesives.Compared to other methods,selecting suitable adhesives has a lower cost and simpler process,and the development of new adhesives can effectively improve the cycling stability of batteries,which has a development prospect suitable for industrialization.Based on the design concept of a dual network structure,this paper selects low-cost polyvinyl alcohol（PVA）,biomass gallic acid（GA,3,4,5-trihydroxybenzoic acid）,and chitosan（CS）as raw materials,and modifies them to cause cross-linking reactions between them.At the same time,hydrogen bonds can be formed between the non-reactive polar groups,thereby forming a hydrogen bond and covalent bond dual network structure adhesive for use in pure silicon anode,which can enable the battery to exhibit better cycle performance.In addition,modified polyvinyl alcohol（EPVA）and carboxylic nitrile rubber latex（XNBR）were compounded for high-quality loaded siliceous oxide anode to explore the impact of the introduction of rubber on their cycle performance.The main research contents are as follows:（1）GA has multiple phenolic hydroxyl groups.After grafting and modifying it with epichlorohydrin（ECH）,its molecular structure carries epoxy groups.This structure has high reactivity and is easy to form a large number of hydrogen bonds.Then,it is used as a cross-linking agent to crosslink and composite with PVA according to different mass ratios to form a dual network structure adhesive.The mechanical property test shows that the adhesive film has a high mechanical strength（89MPa）,and the nanoindentation test shows that the PVA/modified GA（PG）electrode has a large hardness and modulus,indicating that it can effectively inhibit the bulk expansion of the silicon anode.The peel strength shows that the average adhesive force of PG55（PVA:modified GA=5:5,wt%）electrode is 1.28 N,with the highest adhesive strength.Electrochemical testing shows that the PG55 electrode has the most excellent cycling performance,with a coulomb efficiency of 88.92%for the first cycle.After 200 cycles at a mass load of about 1 mg cm-2 and a current density of 0.2 C,it still has a specific capacity of 1822 m Ah g-1.SEM shows that the PG55 electrode has a more complete electrode structure,indicating that the existence of a dual network structure can effectively inhibit the volume expansion of silicon and maintain the integrity of the silicon electrode structure.（2）PVA was modified using ECH to obtain modified polyvinyl alcohol（EPVA）,and then crosslinked with CS at different mass ratios to prepare a dual network adhesive with a certain toughness.The mechanical properties indicate that EPVA has a higher elongation（372%）,which is three times higher than pure PVA.When crosslinked with high modulus CS at a mass ratio of 5:5,it exhibits higher mechanical strength（46 MPa）and better elongation（11%）,The electrochemical performance shows that the crosslinked adhesive exhibits excellent cycling performance under different binder ratios due to the existence of a dual network structure.When the binder ratio is 15%and the mass load is about 0.6 mg cm-2,the first coulomb efficiency is as high as 87.31%.After 100 cycles at a current density of 400 m A g-1,the specific capacity of 2468 m Ah g-1 is remained.After 100 cycles at a current density of 800 m A g-1,the remaining specific capacity is 2305 m Ah g-1,and the capacity retention rate is 64.18%.The analysis of surface micromorphology further indicates that the existence of a dual network structure can better maintain the structural integrity of the electrode and improve the cycle performance of the battery.（3）Based on the above EPVA,XNBR was introduced to react the epoxy group with the carboxyl group,and a super elastic（220%）three-dimensional network adhesive was prepared.Constant-current charge and discharge tests were conducted at high current densities of 0.5C(1C=1600 m A g-1)and 1C under two high mass loads of 2.5-3 mg cm-2 and 3.5-4 mg cm-2,respectively,to explore the impact of the introduction of XNBR on the performance of Si Ox anode.The results show that the introduction of XNBR can effectively improve the specific capacity and the first coulomb efficiency of the battery.When the mass load is 2.5-3 mg cm-2,the remaining specific capacity after 100 cycles at 0.5C and 1C current densities is 362 m Ah g-1 and 354 m Ah g-1,respectively,with the first coulomb efficiency reaching 80.02%.Furthermore,when the mass load is 3.5-4 mg cm-2,there are still 359 m Ah g-1 and 259 m Ah g-1 specific capacities after 100 cycles at0.5C and 1C current density. |
