| With the continuous growth of the electric vehicle and energy storage market,people also put forward higher requirements for energy storage systems.Solid-state lithium metal batteries have received extensive attention due to their advantages in safety,energy density,operating temperature,and cycle performance.As a key component of all-solid-state batteries,the ion-conducting ability of solid-state electrolytes directly determines the performance of all-solid-state batteries.Therefore,combining the advantages of different kinds of solid electrolytes,such as the high ionic conductivity and high mechanical strength of inorganic solid electrolytes and the good interfacial properties and flexibility of polymer electrolytes,to prepare composite solid electrolytes becomes an effective solution for the development of solid-state lithium metal batteries in the future.As to solid-state lithium metal batteries,the development of composite solid-state electrolytes with high ionic conductivity,excellent flexibility,and high mechanical strength is crucial.In addition,the interface impedance between the electrode and the electrolyte,chemical stability,etc.are also key factors.To this end,this dissertation aims to prepare composite solid electrolytes with excellent performance,optimize the electrode-electrolyte interface,and explore the performance of composite solid electrolyte membranes and assembled all-solid-state batteries.The main contents of this disseration are as follows:1.Two Na+superionic conductor(NASICON)-type solid electrolytes were prepared:Li1.3Fe0.3Ti1.7(PO4)3(LFTP)and Li1.3Cr0.3Ti1.7(PO4)3(LCTP).Compared with Li1.3Al0.3Ti1.7(PO4)3(LATP),such two solid electrolytes are more suitable for low temperatures by testing their activation energy.The composite solid electrolytes prepared with LFTP and LCTP have high ionic conductivities of 0.107 and 0.12 m S·cm-1 at 15°C,respectively.Solid-state Li|Li Fe PO4(LFP)batteries with LFTP and LCTP composite electrolytes can deliver initial discharge capacities of 124.5 and 106.7 m Ah·g-1 at a current density of 0.1 C,respectively,with good rate and cycling performance.2.Taking advantage of the strong ion-exchange property of hectorite,lithium salt-modified montmorillonite(Li MNTs)were obtained.An economical composite solid electrolyte with strong ionic conductivity was prepared by combining Li MNTs,polycaprolactone(PCL)and lithium salts.Experiments show that the ionic conductivity of PCL-Li MNT composite solid electrolyte can reach 2.77×10-6 and 1.39×10-5 S·cm-1 at30 and 60?,respectively.At a current of 0.1 C and a temperature of 60?,solid-state Li|LFP and Li|Li Co O2(LCO)batteries with PCL-Li MNT composite electrolyte can provide initial discharge capacities of 159.6 and 125 m Ah·g-1,respectively,with strong rate and cycle performance.3.As the most studied organic polymer electrolyte polyethylene oxide(PEO)and inorganic ceramic electrolyte LATP,they all have their inherent limitations,such as the narrow electrochemical window of PEO,which cannot match the high-voltage cathode,and the side reaction of LATP and lithium metal when they are in contact.In order to combine the advantages of two high ionic conductivity electrolytes,this dissertation prepared a double-layer composite solid-state electrolyte(DSE),where the LATP-dominated electrolyte layer is on the positive side,the PEO polymer electrolyte layer is on the negative side.The overall conductivity is improved by blending polymethyl ethylene carbonate(PPC).The prepared PPC-activated DSE(PPC-DSE)exhibits a high ionic conductivity of 2.55×10-4 S·cm-1 at 60°C.Using PPC-DSE,when paired with LFP and Li Ni0.8Co0.1Mn0.1O2(NCM811)cathodes,Li metal batteries can produce discharge capacities of 159.8 and 192.6 m Ah·g-1 at 0.1 C and 60°C,respectively,with respectable rate and cycling performance.4.In order to further improve the ionic conductivity of DSE,so that it is not limited to the field of high-temperature solid-state batteries,the method of plasticizing with a plasticizer is used to further improve the performance of DSE.In such strategy,bistrifluoroacetamide-DSE(BTFA-DSE)has a high ionic conductivity of 4.4×10-4 S·cm-1 at 25°C.In the solid-state battery system thus designed,the lithium metal battery paired with LFP and NCM811 cathodes can provide specific discharge capacities of 163.3 and219.5 m Ah·g-1 at 0.1 C and 25°C,respectively,with excellent rate and cycling performance.5.This dissertation reports the synthesis of p(dodecafluoroheptyl methacrylate-co-methyl methacrylate)(P(DFMA-co-MMA))as polymer matrix to provide adsorption site for Li+.Moreover,succinonitrile is introduced to suppress polymer crystallization,and long fluorocarbon chains are connected in series to provide long-range channels for Li+transmission.The resultant long-chain fluorocarbon driven hybrid solid polymer electrolyte(LFSPE)membranes can afford an ion conductivity of 6.78×10-4 S·cm-1 at25°C with wide electrochemical stable window(0-4.713 V)and high lithium ion transferencenumber(0.47).Poly(diallyldimethylammonium)-bis(trifluoromethanesulfonyl)imide interlayer is exploited to inhibit side reactions on the Li metal surface and promotes homogeneous Li plating.Thus,steady Li plating/stripping in LFSPE can be achieved under areal capacity of 0.2 m Ah·cm-2 for 2000 h.LFP,LCO and NCM811 solid cells exhibit excellent rate capacity(specific capacity of 138.8,109.6and 145.8 m Ah·g-1 at 1 C,respectively)and long-term cycling stability(98.8%capacity retention after 500 cycles for LFP;81.4%and 71.9%capacity retention after 300 cycles for LCO and NCM811,respectively). |
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