| Modern society benefits a lot from ubiquitous lithium ion batteries(LIBs).However,conventional LIBs employ highly flammable and toxic liquid electrolytes.Safety hazards such as fire or explosion has received the society's continual attention.For the purpose of addressing the safety issues,polyethylene glycol(PEG)based solid polymer electrolytes(PSPEs)are considered as a promising candidate.But PSPEs have never reached the mass production stage,inherent low ionic conductivity and rate cycle performance limited its development.In order to solve those problems,in our previous work,we have synthesized a Si doped polymer electrolyte(Si-PEG)and Si,B doped polymer electrolyte(B-SPEs).However,there still exist some problem in those two polymer electrolytes.?Si-PEG possess undesired mechanical strength which could not effectively suppress lithium dendrites.?Si-PEG possesses poor interface contact with electrode interface,resulting in a large interface impedance.?In B-SPEs system,with the content of boron increase,the lithium transference number does not show much enhancement,a conjecture for the shielding effect is proposed for this problem:when PEG is directly connected to the boron atom,weakly basic PEG will affect Lewis acidic B atoms to capture anions in the lithium salt.This paper aims to solve the problems in Si-PEG and B-SPEs,the main innovations are as follows:?we synthesized high-strength Si-PEG based polymer electrolyte(KSPEs),The amino groups in KSPEs provide more reactive sites for the cross-linking agent 1,6-ethylene isocyanate trimer(HDI),thereby significantly improving the cross-linking density and mechanical strength of KSPEs polymers.?Taking advantage of the rapid reaction of amino groups with HDI crosslinking agent,polymer electrolytes(I-KSPEs)were obtained by in situ crosslinking reaction on the surface of the composite electrode coated with HDI crosslinking agent.The interfacial impedance of LiFePO4/I-KSPEs/Li cell prepared by this method is an order of magnitude lower than that of LiFePO4/KSPEs/Li cell prepared by conventional methods.At 30?and 0.2C rate,the specific discharge capacity of LiFePO4/I-KSPEs/Li cell increased to 122mAhg-1 which was 20%improvement compared with LiFePO4/KSPEs/Li cell.Moreover,after 60 cycles,the capacity of LiFePO4/I-KSPEs/Li cell is still stable.?B-Six-SPEs polymer electrolytes were synthesized by inserting siloxane spacers between B atoms and PEG to explore the shielding effect.The macroscopic properties of the B-Six-SPEs polymer electrolytes,such as ionic conductivities and(tLi+)values are characterized.Raman spectroscopy and 7Li nuclear magnetic resonance(NMR)spectroscopy have been carried out to investigate the ions mobility of lithium salt in the B-Six-PEGs electrolytes.Molecular dynamics(MD)simulation is also used to calculate both the microscopic interaction force between B atom and the anion of Li TFSI(lithium bis(trifluoromethane sulfonimide))and the macroscopic properties of the B-Six-PEGs polymer electrolytes,such as ionic conductivity and(tLi+) value.The theoretical predictions fit very well with the experimental results.If both the concentrations of TFSI-and B atoms in B-Six-PEGs electrolytes are taken into consideration,the normalized diffusion coefficient of TFSI-anions obtained by molecular dynamic(MD)simulation confirms the deshielding effects of siloxane spacing groups on B atoms increase along with x in the B-Six-PEGs polymer electrolytes.This paper is based on the design and improvement of Si-PEG based polymers electrolyte.First,I-KSPEs polymer electrolytes were synthesized via the in-situ reaction strategy on the electrode surface to solve the problem of excessive interface resistance between the polymer electrolyte and the electrode.Secondly,the existence of the shielding effect in the boron-doped Si-PEG based polymer electrolyte was confirmed,and the insertion of a siloxane spacer between the B atom and PEG successfully weakened the effect of PEG on the B atom. |
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