Study On Solid State Lithium Ion Full Battery Based On Sulfur Cathode And Silicon Anode

The unstoppable progress of science and technology and the inevitable trend of the humanity and social development have created a wide demand for a new energy storage system with high energy density,recyclable and environmentally friendly.Traditional fossil energy has gradually been unable to adapt to the trend of highly developed social life due to its drastic reduction of reserves worldwide and excessive pollution to the environment.It is urgent to develop a new high energy density storage system.As an energy storage system with high energy density(2600 wh kg-1)and high theoretical specific capacity(1672 mAh g-1),lithium-sulfur batteries have attracted much attention:in recent years because of their good commercial prospects.However,it should be noted that in the process of its practical application,there are still some problems need to be solved eagerly.Firstly,the intrinsic non-conductivity of lithium polysulfide,which is the intermediate of cathode sulfur material and electrode reaction,will greatly reduce the utilization rate of sulfur in active materiaLSecondly,because the etherelectrolyte will be mostly used in this traditional liquid lithium-sulfur battery system,lithium polysulfide,an intermediate product in the process of electrode reaction,will dissolve in the electrolyte and diffuses to the anode along with the liquid phase,react directly with the anode lithium metal and then adheres to the surface of lithium,resulting in the loss of sulfur in the cathode active material and the serious capacity degradation of the battery.It is the shuttle effect in lithium sulfur batteries.Thirdly,the volume expansion effect of active sulfur materials is about 80%in the process of conversion from electrochemical reaction to lithium polysulfide,and the mechanical properties of the electrode structure will be greatly tested.Fourthly,the uneven growth of litiuitm dendrites will lead to serious safety hazards.In view of the above problems,this paper attempts to propose a solid-state battery system based on sulfur cathode and silicon anode.Firstly,for the sulfur cathodeand the silicon anode which used to replace the lithium cathode material in lithium-sulfur batteries,we improve the cycling performance of the silicon cathode and the sulfur cathode in lithium-sulfur batteries by using the covalently crosslinked polyacrylamide(C-PAM)binder with high mechanical properties and rich polar functional groups,so as to make it hopefully suitable for the entire battery system.Secondly,we further improve the host material of sulfiur cathode,and construct two-dimensional layered sulfur host material based on transition metal sulfide and graphene,in order to optimize the cathode of lithium-sulfiir batteries,increase the sulfur load and enhance the cycle performance of lithium-sulfiur batteries under different current densities.Finally,we studied the compatibility and electrochemical performance of modified PEO-based organic solid-state electrolytes for traditional lithium-ion batteries,and tried to find all-solid-state organic electrolyte systems suitable for such solid-state batteries we mentioned above.By means of XRD,FTIR,SEM,TEM,Raman and TG,the compositions,microstructures and functional groups of the materials prepared by the above three improved methods were analyzed.On the premise of revealing the microstructural characteristics of various materials and the role of functional groups,we further tested the electrochemical performance of the battery systems in their respective applications,such as constant current charging and discharging,cyclic voltammetry,AC impedance and so on.Our research work mainly covers the following aspects:(1)Preparation of covalently crosslinked polyacrylamide with high mechanical properties andrich polar functional groups as binder for silicon anode and sulfur cathode of lithium ion batteries.On the one hand,polar functional groups can benefitto restrain lithium polysulfide shuttle in battery cycle.On the other hand,binders with high mechanical properties will play an active role in maintaining the integrity of the electrodes and enhancing the mechanical properties of the electrodes.The results showed that the covalently crosslinked polyacrylamide with crosslinking degree of 0.1%and concentration of 5%could be stretched to more than 6.1 times the original length.By means of SEM and other characterization methods,the integrity of the electrode laminate can be well maintained by using this polyacrylamide as the binder for the silicon anode of lithium ion batteries.The capacity of assembled semi-battery is 2843 mAh g-1 after 100 cycles at 0.1 C,and the corresponding capacity retention rate is 90.1%.In the C-rate test,at the C-rate of 1 C,5 C,10 C and 20 C,the reversible capacity of the battery is 2736.3,2547.7,2443.6 and 2315.4 mAh g-l,respectively.Batteries not only perform well in cycle performance test,but also exhibit outstanding reversible capacity under different C-rate test conditions.In the application of sulfur cathode in lithium-sulfur batteries,we proved that this binder can play a positive role in inhibiting lithium polysulfide shuttle by applying in-situ Raman characterization method.In terms of battery performance,when the sulfur load is about 1 mg cm-2 and the C-rate is 1 C,the capacity of the battery after 200 cycles is 588 mAh g-1,the corresponding capacity retention rate is 97.9%,and the coulombic efficiency is more than 98%.At 3 C,the reversible capacity of the battery is about 470 mAh g-1.(2)Layered transition metal sulfide vanadium disulfide(VS2)was grown on the surface of reduced graphene oxide by in situ self-assembly method.Two-dimensional graphene-vanadium disulfide composite sulfur host material(G-VS2)was constructed and used in lithium-sulfur batteries.The experimental results show that the two-dimensional host material G-VS2 has obvious inhibitory effeect on the shuttle effect of lithium polysulfide.Moreover,on the surface of two-dimensional G-VS2,the conversion rate of lithium polysulfide can be accelerated,which is conducive to increasing the utilization rate of sulfur active materials.The reversible capacity of the battery can reach 950 mAh g-1 and 800 mAh g-1 at 1 C and 2 C,respectively.At 5 C,the capacity of the battery after 300 cycles is about 532 mAh g-1.The two-dimensional composite material can also show good adaptability for the application of high load lithium-sulfur batteries(5 mg cm-2).(3)Polyethylene oxide(PEO)was used as the organic solid electrolyte matrix,and polymaleic acid(HPMA)additive with dispersive function was added to PEO-based electrolyte to reduce the crystallinity of PEO-based electrolyte at room temperature.Finally,solid electrolyte with high ionic conductivity at room temperature was obtained.After electrochemical testing of LFP cathode,we proved that the addition of this HPMA material can effectively improve the conductivity of PEO-based organic solid electrolyte at room temperature,and make the battery work normally at room temperature.