CN117438644A - Preparation method of novel solid electrolyte based on doped lithium aluminum titanium phosphate modification - Google Patents
Preparation method of novel solid electrolyte based on doped lithium aluminum titanium phosphate modification Download PDFInfo
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- 229910000664 lithium aluminum titanium phosphates (LATP) Inorganic materials 0.000 title claims abstract description 86
- 239000007784 solid electrolyte Substances 0.000 title claims abstract description 67
- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- CVJYOKLQNGVTIS-UHFFFAOYSA-K aluminum;lithium;titanium(4+);phosphate Chemical compound [Li+].[Al+3].[Ti+4].[O-]P([O-])([O-])=O CVJYOKLQNGVTIS-UHFFFAOYSA-K 0.000 title claims abstract description 11
- 230000004048 modification Effects 0.000 title claims abstract description 10
- 238000012986 modification Methods 0.000 title claims abstract description 10
- 239000000843 powder Substances 0.000 claims abstract description 36
- 239000003792 electrolyte Substances 0.000 claims abstract description 31
- 229910003473 lithium bis(trifluoromethanesulfonyl)imide Inorganic materials 0.000 claims abstract description 17
- QSZMZKBZAYQGRS-UHFFFAOYSA-N lithium;bis(trifluoromethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)F QSZMZKBZAYQGRS-UHFFFAOYSA-N 0.000 claims abstract description 16
- 238000003756 stirring Methods 0.000 claims abstract description 14
- 239000003153 chemical reaction reagent Substances 0.000 claims abstract description 12
- 238000001035 drying Methods 0.000 claims abstract description 12
- 239000002904 solvent Substances 0.000 claims abstract description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 11
- 239000011259 mixed solution Substances 0.000 claims abstract description 10
- -1 polytetrafluoroethylene Polymers 0.000 claims abstract description 5
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims abstract description 4
- 239000004810 polytetrafluoroethylene Substances 0.000 claims abstract description 4
- 238000000034 method Methods 0.000 claims description 11
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical group CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 9
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 6
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 claims description 6
- 239000002243 precursor Substances 0.000 claims description 6
- 238000005245 sintering Methods 0.000 claims description 6
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 239000007790 solid phase Substances 0.000 claims description 4
- 239000000243 solution Substances 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 3
- 238000001354 calcination Methods 0.000 claims description 2
- 238000003801 milling Methods 0.000 claims description 2
- 235000011837 pasties Nutrition 0.000 claims description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims 1
- 238000003760 magnetic stirring Methods 0.000 claims 1
- 229920000642 polymer Polymers 0.000 abstract description 65
- 239000002131 composite material Substances 0.000 abstract description 45
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 24
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 24
- 239000007787 solid Substances 0.000 abstract description 7
- 239000012528 membrane Substances 0.000 description 46
- 238000012360 testing method Methods 0.000 description 27
- 229920003171 Poly (ethylene oxide) Polymers 0.000 description 16
- 229910052744 lithium Inorganic materials 0.000 description 10
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 8
- 150000002500 ions Chemical class 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 239000005518 polymer electrolyte Substances 0.000 description 6
- 239000011889 copper foil Substances 0.000 description 5
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 4
- 229910052493 LiFePO4 Inorganic materials 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 4
- 125000004122 cyclic group Chemical group 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 238000000576 coating method Methods 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 230000001351 cycling effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000002161 passivation Methods 0.000 description 3
- 238000006479 redox reaction Methods 0.000 description 3
- 125000006850 spacer group Chemical group 0.000 description 3
- 230000037303 wrinkles Effects 0.000 description 3
- 229910006270 Li—Li Inorganic materials 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 239000003814 drug Substances 0.000 description 2
- 239000007772 electrode material Substances 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 238000011049 filling Methods 0.000 description 2
- 238000001453 impedance spectrum Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000004502 linear sweep voltammetry Methods 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 229910001251 solid state electrolyte alloy Inorganic materials 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 238000013112 stability test Methods 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 230000004913 activation Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- QKIUAMUSENSFQQ-UHFFFAOYSA-N dimethylazanide Chemical compound C[N-]C QKIUAMUSENSFQQ-UHFFFAOYSA-N 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000013618 particulate matter Substances 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000002411 thermogravimetry Methods 0.000 description 1
- 238000001757 thermogravimetry curve Methods 0.000 description 1
- 238000012876 topography Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0082—Organic polymers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0085—Immobilising or gelification of electrolyte
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Electrochemistry (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Inorganic Chemistry (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Physics & Mathematics (AREA)
- Materials Engineering (AREA)
- Secondary Cells (AREA)
Abstract
The invention relates to a preparation method of a novel solid electrolyte based on doped lithium aluminum titanium phosphate modification, which comprises the steps of adding a solvent into a reagent bottle, adding LiTFSI powder, continuously stirring, adding PEO powder after LiTFSI is completely dissolved, magnetically stirring for 20-30h in a water bath at 25-35 ℃, adding LATP powder, continuously stirring for 20-30h, after stirring uniformly, drying the mixed solution in a polytetrafluoroethylene dish at 25-35 ℃ for 10-15h, and then drying at 45-65 ℃ for 10-15h to obtain an electrolyte film. The first discharge specific capacity of the solid lithium ion battery manufactured by adopting the composite polymer solid electrolyte is increased from 130mAh/g to 160mAh/g, the coulomb efficiency is increased from 77% to 99%, and the comprehensive performance is obviously improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a novel solid electrolyte based on doped titanium aluminum lithium phosphate modification.
Background
The lithium ion battery has the advantages of high energy density, no memory effect and the like, is widely used in the fields of electronic equipment, transportation and the like, and the development of solid-state batteries based on solid-state electrolytes is one of the necessary trends for improving the comprehensive performance of the lithium ion battery. The polymer solid electrolyte has the advantages of simple preparation, good film forming property, flexible application and the like, is expected to obviously improve the performances of the lithium ion battery, such as safety, energy density, cycling stability and the like, but has the defects of low conductivity, low mechanical strength, poor thermal stability and the like.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method of a novel solid electrolyte based on doped lithium aluminum titanium phosphate modification. The polymer solid electrolyte (PEO-LITFSI) is modified by utilizing Lithium Aluminum Titanium Phosphate (LATP) particles with higher ionic conductivity and thermal stability, so that the ionic conductivity, mechanical and thermal stability at room temperature are improved.
The technical scheme adopted for solving the technical problems is as follows:
a preparation method of a novel solid electrolyte based on doped lithium aluminum titanium phosphate modification comprises the steps of adding a solvent into a reagent bottle, slowly adding LiTFSI powder, continuously stirring, slowly adding PEO powder after LiTFSI is completely dissolved, magnetically stirring for 20-30h in a water bath at 25-35 ℃, and adding LATP powder, wherein the mass ratio of LiTFSI to PEO to LATP is as follows: 2-3: 1: and (3) continuously stirring the solvent for 20 to 30 hours, wherein the concentration of LiTFSI is 0.03 to 0.45 and 0.05g/ml, and after the solvent is uniformly stirred, drying the mixed solution in a polytetrafluoroethylene dish at 25 to 35 ℃ for 10 to 15 hours, and then drying the mixed solution at 45 to 65 ℃ for 10 to 15 hours to obtain the electrolyte film.
Further, the LATP is prepared by a solid phase sintering method, and the steps are as follows: first LiOH.H 2 O is dissolved in pure water and stirred uniformly; subsequently, al is stirred 2 O 3 ，TiO 2 And H 3 PO 4 Adding the three substances into the solution according to the mass ratio of 1:5-7:14-15; placing the mixture in a crucible and drying at 160-200deg.C to remove excessive water until a paste with high viscosity is formed; calcining the pasty reagent in the crucible at 650-750 ℃ to obtain LATP precursor powder; mechanically milling the obtained precursor powder in a high-energy ball mill for 8-12 hours by using zirconia balls; sintering the ground powder in air at 600-800 ℃ for 10-15h to form compact LATP.
Further, the mass ratio of LiTFSI to PEO to LATP is: 2.76:1:0.04.
further, the solvent is acetonitrile.
Further, liTFSI was present at a concentration of 0.02g/ml solvent.
Further, PEO powder, liTFSI powder, LATP powder are dried in a constant temperature oven at 45-60deg.C for 1-3h before use.
Further, al 2 O 3 ，TiO 2 And H 3 PO 4 The mass ratio is 1:6.3:14.4.
The invention has the advantages and positive effects that:
1. the LATP nano-particles are prepared by adopting a solid phase sintering method, and the average particle size of the LATP nano-particles is about 0.7um; the ionic conductivity at room temperature is about 2.19X10-4S/cm; it is stable at 800 deg.c and has no decomposition and high heat stability.
2. The LATP modified composite polymer solid electrolyte membrane is prepared by adopting a solution casting method, and has good comprehensive performance under the doping concentration of 1 weight percent. The doping of LATP can reduce the crystallinity of the polymer electrolyte membrane, improve the ion conductivity, and improve the ion conductivity from 4.38X10-8S/cm to 1.15X10-5S/cm at normal temperature; has excellent thermal stability at 350 ℃; the mechanical strength is good, and the ultimate stress can reach 3MPa; the electrochemical window increases from 4.5V to 6.0V; in the lithium-on-battery test, the voltage at 50uA is still kept at 0.01V after 14000min, and the stability is good.
3. The invention adopts the composite polymer solid electrolyte to manufacture the solid lithium ion battery. When the temperature is increased from 50 ℃ to 60 ℃, the impedance of the battery is reduced from 900 omega to 500 omega; the initial discharge specific capacity of the battery is increased from 130mAh/g to 160mAh/g at 0.1C, the coulomb efficiency is increased from 77% to 99%, and the comprehensive performance is obviously improved.
Drawings
Fig. 1 is a schematic diagram of a battery mounting sequence;
FIG. 2-1 is an XRD pattern for a composite polymer solid electrolyte with LATP doping levels of 0wt%,1wt%,5wt%, respectively;
FIGS. 2-2 (a) (b) (c) are SEM images of the surfaces of the composite polymer solid electrolyte membrane having LATP contents of 0wt%,1wt% and 5wt%, respectively, and (d) (e) (f) are SEM images of cross sections of the composite polymer solid electrolyte membrane having LATP contents of 0wt%,1wt% and 5wt%, respectively;
FIGS. 2-3 are graphs of conductivity versus temperature for samples of different doping concentrations at different temperatures;
FIGS. 2-4 (a) (b) (c) are optical pictures of samples stored at 160℃for 0h,0.5h, and 3h, respectively;
FIGS. 2-5 are thermogravimetric analysis plots of a composite polymer solid electrolyte with a LATP doping level of 5wt% and a commercial separator;
FIGS. 2-6 are tensile test stress-strain curves for polymer solid electrolyte membrane samples;
FIGS. 2-7 are electrochemical window test curves for samples of different doping concentrations;
FIGS. 2-8 are changes in conductivity of electrolytes having doping concentrations of 0wt%,5wt% and 10wt%, respectively, after a period of time;
FIGS. 2-9 (a) are constant current cycling charge-discharge tests of PEO-LTP00 electrolyte membranes and (b) are constant current cycling charge-discharge tests of PEO-LTP05 electrolyte membranes;
FIGS. 3-1 (a) (b) (c) (d) are CV cycle curves of cells assembled from composite polymer solid electrolyte membranes having LATP doping levels of 0wt%,1wt%,5wt%,10wt%, respectively;
FIG. 3-2 is a graph showing the first charge-discharge capacity change at 0.1C for assembled cells with samples of different doping concentrations;
FIGS. 3-3 (a) are EIS diagrams of a battery at 50deg.C, (b) are EIS diagrams of a battery at 60deg.C, and (c) are EIS diagrams of a battery at 60deg.C after 10 times of cyclic charge and discharge.
Detailed Description
The invention is further illustrated by the following examples, which are intended to be illustrative only and not limiting in any way.
Example 1
A preparation method of a novel solid electrolyte based on doped lithium aluminum titanium phosphate modification is characterized in that LATP is used for doping modification of the polymer solid electrolyte, and in order to study the influence of the filling amount of the LATP on the performance of the polymer solid electrolyte, the filling ratio of the LATP is set, and LATP with mass fractions of 1wt%,5wt% and 10wt% is added respectively.
The method comprises the following steps:
three parts of 1.835g PEO (polyethylene oxide) powder, 0.665g LiTFSI (lithium bistrifluoromethane sulfonyl imide) powder, and 0.025g,0.132g and 0.278g LATP powder were weighed respectively and dried in a constant temperature oven at 50deg.C for 2h. 36mL of acetonitrile is measured by a measuring cylinder and poured into three clean reagent bottles, and then magnetons are added and stirred on a magnetic stirrer at normal temperature.
After the medicine is dried, liTFSI powder is slowly added into each reagent bottle, and is continuously stirred, PEO powder is slowly added after LiTFSI is completely dissolved, and the mixture is magnetically stirred for 24 hours in a water bath at 30 ℃.
0.025g,0.132g,0.278g LATP powder were each slowly added to three reagent bottles and stirring was continued for 24h.
After stirring uniformly, the mixed solutions were poured into polytetrafluoroethylene dishes of 10cm diameter, dried at 30℃for 12 hours, and dried at 50℃for 12 hours, to give dried electrolyte films of 1wt%,5wt% and 10wt% LATP, respectively, designated PEO-LTP01, PEO-LTP05 and PEO-LTP10.
Wherein Lithium Aluminum Titanium Phosphate (LATP) is prepared by a solid phase sintering method, and the steps are as follows:
first LiOH.H 2 O is dissolved in pure water and stirred uniformly on a magnetic stirrer. Subsequently, al is stirred magnetically 2 O 3 ，TiO 2 And H 3 PO 4 The three substances are respectively added into the solution according to the mass ratio of 1:6.3:14.4. The mixture was placed in a crucible and dried at 180 ℃ to remove excess water until a paste with very high viscosity was formed. The paste reagent in the crucible was calcined at 700 ℃ to obtain LATP precursor powder. The obtained precursor powder was mechanically milled in a high-energy ball mill for 10 hours using zirconia balls having a diameter of 12 mm. The milled powder was sintered in air at 700 ℃ for 12h to form a dense LATP electrolyte sample.
Comparative example 1
The difference from example 1 is that Lithium Aluminum Titanium Phosphate (LATP) was not doped, and a composite polymer solid electrolyte membrane PEO-LTP00 was obtained.
Performance testing
Preparing a positive electrode of a lithium ion battery: the active material is LiFePO 4 . Firstly, preparing a mixed solution of a composite polymer electrode material by adopting a stirring method, wherein the mixed solution system is 60wt%LiFePO4, 30wt%PEO-LiTFSI and 10wt% CB, then uniformly coating the mixed solution on the surface of a copper foil by adopting a coating method, and finally, drying, wherein the main experimental steps are as follows:
1) 500mg LiFePO4, 183.5mg PEO,66.5mg LiTFSI and 83.33mg CB powder were weighed out separately by electronic day and placed in a constant temperature oven for drying at 50℃for 2 hours. 3.6ml of LDMF (dimethyl amide) is measured by a measuring cylinder, poured into a clean reagent bottle, and then a magneton is added and stirred on a magnetic stirrer at normal temperature.
2) After the medicine is dried, liTFSI powder is slowly added into a reagent bottle, and is continuously stirred, PEO powder is slowly added after LiTFSI is completely dissolved, and the mixture is magnetically stirred for 24 hours in a water bath at 40 ℃.
3) Respectively and slowly adding LiFePO4 and CB powder into the reagent bottle, and continuously stirring for 24 hours until the LiFePO4 and CB powder are uniformly dispersed.
4) The mixed solution was coated on a copper foil with a 300um doctor blade at a coating area of 100cm2 and an active material areal density of 5mg/cm2 (area capacity of 0.75mAh/cm 2).
5) And (5) placing the coated copper foil into a drying oven and drying at 50 ℃ to obtain the composite polymer electrode.
Manufacturing a solid-state lithium ion battery: the positive electrode is the composite polymer electrode prepared above, the electrolyte is the composite polymer solid electrolyte membrane prepared above, and the negative electrode is a lithium sheet. Cutting the electrolyte membrane into a circular sheet with the diameter of 16cm by a tablet press, cutting the anode copper foil into a circular sheet with the diameter of 12cm, and manufacturing the lithium ion battery by a button cell sealing machine in an inert gas environment in a glove box. The internal structure of the battery is shown in fig. 1:
the internal structure of the cell fabricated in the subsequent EIS test on the solid electrolyte membrane was: negative electrode shell-spring piece-1 mm gasket-PEO electrolyte sheet-LiFePO 4 Copper foil-1 mm spacer-positive electrode shell;
the internal structure of the prepared Li-Li pair battery is as follows: negative electrode shell-spring piece-0.5 mm gasket-lithium foil-PEO electrolyte piece-lithium foil-0.5 mm gasket-positive electrode shell;
the internal structure of the battery fabricated in the CV test is: negative electrode shell-spring piece-0.5 mm gasket-lithium foil-PEO electrolyte piece-LiFePO 4 Copper foil-1 mm spacer-positive electrode shell.
1. Structural characterization
XRD diffraction patterns of the polymer solid electrolyte and the composite polymer solid electrolyte doped with LATP are shown in fig. 2-1. It can be seen that the XRD diffraction pattern of the PEO-based polymer solid electrolyte without doped LATP has more obvious diffraction peaks, and can be judged that a very polycrystalline phase exists in the PEO-based polymer solid electrolyte, the crystallinity is higher, and the chain segment movement in the polymer can be blocked to a certain extent, so that the ionic conductivity is reduced. The XRD pattern of the composite polymer solid electrolyte doped with 1wt% and 5wt% of LATP has no diffraction peak, so that the composite polymer solid electrolyte can be judged to be amorphous, the migration movement of lithium ions is facilitated, and the conductivity of the composite polymer electrolyte is improved.
2. Characterization of topography
Fig. 2-2 (a), fig. 2-2 (b) and fig. 2-2 (c) are SEM images of the surfaces of the composite polymer solid electrolyte membrane having LATP contents of 0wt%,1wt% and 5wt%, respectively, fig. 2-2 (d), fig. 2-2 (e) and fig. 2-2 (f) are SEM images at the cross-sections of the corresponding composite polymer solid electrolyte membrane, respectively.
From fig. 2-2 (a) and fig. 2-2 (d), it can be seen that the undoped polymer solid electrolyte membrane has more surface wrinkles without voids, a dense cross section with more cracks, and a membrane thickness of 198.16 μm. As can be seen from FIGS. 2-2 (b) and 2-2 (e), the composite polymer electrolyte membrane doped with 1wt% LATP has more surface wrinkles, no voids, particulate matter accumulated on the surface, a compact cross section, no cracks, and a membrane thickness of 152.70. Mu.m. It is explained that the addition of LATP makes the surface of the electrolyte membrane rougher, but can increase the density of the membrane, making its strength increase without crack occurrence. As can be seen from FIGS. 2-2 (c) and 2-2 (f), the surface of the composite polymer electrolyte membrane doped with 5wt% LATP has more wrinkles, no pores, a large amount of particulate matters are gathered on the surface, large agglomerated particles are locally formed, the cross section is compact, a small amount of cracks are formed, and the thickness of the membrane is 141.04 μm. The larger the amount of LATP added, the coarser the surface of the film and the denser the film, but the agglomeration of LATP particles doped in the film and the cracking caused by the lack of uniform dispersion of LATP powder during stirring. Thus, it can be concluded that doping LATP in an appropriate amount improves the mechanical properties of the polymer solid electrolyte membrane, but may result in poor interfacial properties of the membrane, increasing the interfacial resistance to some extent.
In a lithium ion battery, the alternating current impedance of an electrolyte membrane is important to the influence of the performance of the electrolyte membrane, and the higher the ion conductivity is, the larger the discharge current of the corresponding lithium ion battery is, and the lower the internal consumption of the battery is, the higher the cyclic charge-discharge efficiency is. It is therefore necessary to test the electrochemical resistance of the prepared composite polymer solid electrolyte membrane. To analyze the effect of the doping of the solid electrolyte LATP on the ac impedance of the composite polymer solid electrolyte membrane, we performed EIS tests on the composite polymer solid electrolyte membrane samples having LATP contents of 0wt%,1wt%,5wt% and 10wt%, respectively, and studied the effect of temperature changes on the ac impedance thereof.
TABLE 1 conductivity of samples of different doping concentrations at different temperatures
According to the measured EIS alternating current impedance spectrum, the total impedance of each sample at different temperatures is obtained, and then the ion conductivity of each sample is calculated according to a conductivity calculation formula. The results of the ion conductivity calculations for each sample are set forth in Table 3-1.
According to the arrhenius equation:
σ＝Aexp(-E/kT)
where σ is the ionic conductivity, k is the Boltzmann constant, E is the conductivity activation energy, and A is the conductivity constant.
Taking the logarithm of the ionic conductivity data in the table to obtain the value of Log sigma, a curve of the variation of the Log sigma of different samples along with 1/T can be made, as shown in figures 2-3.
It can be seen from the figure that the ionic conductivity of the composite polymer solid state electrolyte of different LATP doping ratios increases with increasing temperature and the rate at which the ionic conductivity increases with increasing temperature becomes smaller in the higher temperature region. This suggests that the carriers (li+) in the polymer matrix are activated after being excited by heat, that the carrier concentration increases, and that the film gradually softens better contact with the electrode after the temperature increases, reducing the interface resistance. The higher the temperature, the greater the ionic conductivity of the composite polymer electrolyte.
Wherein, in the normal temperature range, the ionic conductivity of the polymer solid electrolyte which is not doped with LATP is the lowest, which is about 5.35 multiplied by 10 < -6 > S/cm. The ionic conductivity of the composite polymer solid electrolyte with LATP doping level of 1wt% is highest, about 1.15X10-5S/cm. The ion conductivities of the four samples are sequentially from large to small: PEO-LTP01> PEO-LTP05> PEO-LTP10> PEO-LTP00. This suggests that after LATP addition, the interaction between the filler surface and the lithium salt promotes dissociation of the lithium salt molecules, li+ becomes a carrier, thereby increasing the conductivity of the polymer solid electrolyte. However, too much amount may cause a large amount of aggregation of the LATP filler, and the internal crystallinity of the polymer is still high, so that the segment movement is affected, and the effect of increasing the ionic conductivity is not obvious. It is also possible that too much is added to make the membrane too dense, which is detrimental to lithium ion conduction. In this experiment 1wt% is the optimal doping concentration of LATP.
4. Thermal stability test
FIGS. 2-4 (a) (b) (c) are photographs of four samples of PEO-LTP00, PEO-LTP01, PEO-LTP05, PEO-LTP10 after storage at 160℃for 0h,0.5h and 3h, respectively. It can be seen from the figure that the polymer solid electrolyte membrane, which is not doped with LATP, has begun to melt and shrink at a high temperature of 160 ℃ and the mechanical structure has been destroyed. The solid electrolyte membrane of the composite polymer doped with LATP still maintains the original shape and size after being stored at high temperature, and does not have the phenomenon of melting. This illustrates that the doping of LATP can significantly improve the thermal stability of the polymer solid state electrolyte.
Fig. 2-5 are graphs comparing thermogravimetric analysis curves of an experimentally prepared 5wt% latp doped composite polymer solid electrolyte membrane with a commercial polyethylene lithium ion battery separator manufactured by Celgard corporation. From the figure, it can be seen that commercial lithium ion battery separators begin to fail by weight reduction decomposition at a high temperature of 450 ℃. And the composite polymer solid electrolyte membrane starts to decompose and fail at about 350 ℃, so that the working temperature of the composite polymer solid electrolyte membrane can be judged not to exceed 350 ℃. Compared with commercial lithium ion battery diaphragms, the thermal stability of the lithium ion battery diaphragm has a certain gap, and further research and improvement are needed.
5. Mechanical stability test
To test the mechanical properties of the composite polymer solid electrolyte, we performed tensile testing on a standard sample with a width of 2mm and a length of 13mm using a universal tensile machine. Fig. 2-6 are stress-strain curves for polymer solid state electrolyte samples without doped LATP, from which it can be seen that the ultimate stress of the sample is reached when the stress is around 3MPa, at which point the ultimate strain is about 1500%.
The data of ultimate stress, ultimate strain, elongation and the like of the composite polymer electrolyte membrane of other doping ratios obtained by the test are shown in table 2. From the data it can be analyzed that the doping of LATP reduces the ultimate stress of the composite polymer solid electrolyte to some extent. Of the three samples of different doping concentrations, the ultimate stress was the greatest and the intensity the greatest when the doping amount was 1 wt%. The ultimate stress of the sample is instead reduced to some extent as the doping ratio increases, which is manifested as a decrease in strength. Although the elongation and ultimate strain of the sample doped at 10wt% are large, the ultimate stress is not increased correspondingly, and the yield phenomenon of the material is shown. Therefore, the composite polymer solid electrolyte membrane with the LATP doping amount of 1wt% can be judged to have the greatest strength and the best mechanical property.
Table 2 sample mechanical properties test data
6. Electrochemical window testing
We performed electrochemical window testing of composite polymer solid state electrolytes using linear sweep voltammetry LSV, as shown in fig. 2-7. From this figure, it can be seen that the electrochemical stability of the composite polymer solid electrolyte with a LATP doping level of 1wt% is best, no redox reaction occurs at voltages exceeding 6V, the electrochemical window is wide, and multiple electrode materials can be matched. LATP doping levels of 0wt%,5wt% and 10wt% of the composite polymer solid electrolyte have electrochemical windows of about 0V to 4.5V, and have slightly poorer electrochemical stability than PEO-LTP 01.
7. Lithium-to-battery performance test
In order to further study the performance of the composite polymer solid electrolyte, the prepared Li-Li pair battery has the following internal structure: negative electrode shell-spring leaf-0.5 mm spacer-lithium foil-PEO electrolyte sheet-lithium foil-0.5 mm spacer-positive electrode shell. After a period of time, the conductivity is improved to some extent, as shown in fig. 2-8. The polymer solid electrolyte with LATP doping levels of 0wt% and 10wt% decreased in electrical conductivity to about 2.8X10-7S/cm followed by an increase to about 4.8X10-7S/cm after standing for a period of time. The conductivity of the polymer solid electrolyte with LATP doping level of 5wt% is kept stable first, the variation is small, and then the conductivity is increased to 5.4X10-7S/cm. This shows that the polymer solid electrolyte with a doping amount of 5wt% is better in stability after a long-term standing and higher in ionic conductivity.
In order to further test the stability of the composite polymer solid electrolyte membrane and the adsorption capacity and conduction capacity of lithium ions, constant current cycle charge and discharge are carried out on the lithium pair battery. Fig. 2 to 9 (a) are test results of polymer solid electrolyte membranes without doped LATP, and fig. 2 to 9 (b) are test results of composite polymer solid electrolyte membranes with a doping amount of 5 wt%. As can be seen from the graph, under the constant-current charge-discharge test at 60 ℃, the potential of the two electrodes of the PEO-LTP05 film is lower, and lithium ions can be deposited and peeled off on the surface of the electrolyte film more quickly. The voltage at 50uA remained at 0.01V after 14000 min. It can thus be stated that the doping of LATP can increase the stability of the polymer solid electrolyte and increase the adsorption capacity and ionic conductivity of ions.
8. Cyclic voltammetry test
After testing the properties of the composite polymer solid electrolyte membrane, we fabricated a polymer solid lithium ion battery and tested the CV of the battery with an electrochemical workstation, using the battery structure: negative electrode shell-spring piece-0.5 mm gasket-lithium foil-PEO electrolyte sheet-LiFePO 4 copper foil-1 mm gasket-positive electrode shell, positive electrode material is lithium iron phosphate coated copper foil negative electrode material is lithium sheet. The test temperature was 60℃and the scan range was between 2.5V and 3.8V, with a scan rate of 0.2mV/s. The test results are shown in FIG. 3-1.
As can be seen from the graph, as the number of cycles increases, the current value of the redox peak becomes smaller and the impedance of the battery becomes larger. This is probably because as the redox reaction proceeds at the electrode, a thicker and thicker passivation layer is gradually formed between the electrode and the electrolyte, so that the interface resistance between the electrolyte and the electrode becomes large, resulting in gradual reduction of the redox reaction. FIG. 3-1 (b) shows the maximum redox peak current in the four CV cycle diagrams, and it can be demonstrated that the cell fabricated with the composite polymer solid electrolyte membrane having LATP doping amount of 1wt% has better interface properties.
9. Charge-discharge cycle performance test
After testing the cyclic CV curve of the battery, we performed constant current cyclic charge and discharge tests on the battery at a rate of 0.1C using a blue cell test system, as shown in FIG. 3-2. The standard specific capacity of the lithium iron phosphate positive electrode material is 150mAh g-1, and as can be seen from the graph, the charge-discharge capacity of the composite polymer solid electrolyte battery with the LATP doping amount of 5wt% is about 0.7mAh at most (the discharge specific capacity is about 160mAh/g and the coulombic efficiency is about 99%), and the capacity of the solid electrolyte battery without the LATP is the lowest (the discharge specific capacity is about 130mAh/g and the coulombic efficiency is about 77%), which indicates that the doping of the LATP can improve the capacity of the battery to a certain extent. But the capacity of the battery is also low compared to the capacity of other commercial batteries. This is probably because a dense passivation film is formed by lithium ion reaction deposition at the electrolyte interface at the time of the first charge and discharge, lithium ions are difficult to permeate in a short time, and also because the charge and discharge rate is excessively large, and the structure of the solid electrolyte membrane is destroyed.
10. AC impedance testing
And finally, performing EIS test on the assembled battery. We tested the samples at 50℃and 60℃respectively, with the electrochemical workstation frequency ranging from 100mHz to 1 MHz. The alternating current impedance spectrum is shown in figures 3-3.
As can be seen from fig. 3-3 (a), the impedance of the electrolyte sample with a doping level of 1wt% of LATP is lowest, about 1000 ohms, at 50 ℃. The second samples were doped at 5wt% and 10wt%, the lowest being the electrolyte samples without doped LATP. It can be thus concluded that a cell assembled from a solid state electrolyte of LATP polymer with a doping level of 1wt% has better electrochemical performance.
FIGS. 3-3 (b) are EIS graphs of samples measured at 60deg.C, wherein the relation between the impedance of each sample and the doping amount of LATP is the same as that measured at 50deg.C, and the impedance of the electrolyte sample having a doping amount of LATP of 1wt% is at least 500 ohm. But overall the impedance becomes smaller, which means that at higher temperatures the electrochemical performance of the cell made of the composite polymer solid electrolyte is better, which is consistent with the temperature performance of the electrolyte membrane.
Fig. 3-3 (c) are ac impedance diagrams at 60 c after 10 cycles of charge and discharge of the battery are completed. The figure shows that the internal resistance of the battery increases greatly after charge and discharge, probably because deposition of lithium during charge and discharge causes a passivation layer to be formed between the electrolyte membrane and the electrode, which makes migration of lithium ions hindered to cause a great increase in the internal resistance of the battery. Thus, the problem of interfacial contact between the solid electrolyte membrane and the electrodes remains largely limiting the improvement in performance of solid electrolyte lithium ion batteries.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that variations and modifications can be made without departing from the scope of the invention.
Claims (7)
1. A preparation method of a novel solid electrolyte based on doped lithium aluminum titanium phosphate modification is characterized in that a solvent is added into a reagent bottle, liTFSI powder is slowly added, stirring is continued, PEO powder is slowly added after LiTFSI is completely dissolved, magnetic stirring is carried out for 20-30h under a water bath at 25-35 ℃, LATP powder is added, and the mass ratio of LiTFSI to PEO and LATP is as follows: 2-3: 1: and (3) continuously stirring the solvent for 20 to 30 hours, wherein the concentration of LiTFSI is 0.03 to 0.45 and 0.05g/ml, and after the solvent is uniformly stirred, drying the mixed solution in a polytetrafluoroethylene dish at 25 to 35 ℃ for 10 to 15 hours, and then drying the mixed solution at 45 to 65 ℃ for 10 to 15 hours to obtain the electrolyte film.
2. The preparation method according to claim 1, characterized in that LATP is prepared by a solid phase sintering method, comprising the steps of: first LiOH.H 2 O is dissolved in pure water and stirred uniformly; subsequently, al is stirred 2 O 3 ，TiO 2 And H 3 PO 4 Adding the three substances into the solution according to the mass ratio of 1:5-7:14-15; placing the mixture in a crucible and drying at 160-200deg.C to remove excessive water until a paste with high viscosity is formed; calcining the pasty reagent in the crucible at 650-750 ℃ to obtain LATP precursor powder; mechanically milling the obtained precursor powder in a high-energy ball mill for 8-12 hours by using zirconia balls; sintering the ground powder in air at 600-800 ℃ for 10-15h to form compact LATP.
3. The preparation method according to claim 2, wherein the mass ratio of LiTFSI to PEO and LATP is: 2.76:1:0.04.
4. a method of preparation according to claim 3, wherein the solvent is acetonitrile.
5. The process of claim 4, wherein LiTFSI is present in a concentration of 0.02g/ml solvent.
6. The method of claim 5, wherein the PEO powder, liTFSI powder, LATP powder are dried in a constant temperature oven at 45-60deg.C for 1-3h before use.
7. The method according to claim 6, wherein Al 2 O 3 ，TiO 2 And H 3 PO 4 The mass ratio is 1:6.3:14.4.
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