CN115842159A - Polymer-based composite solid electrolyte and preparation method and application thereof - Google Patents
Polymer-based composite solid electrolyte and preparation method and application thereof Download PDFInfo
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- CN115842159A CN115842159A CN202111117866.7A CN202111117866A CN115842159A CN 115842159 A CN115842159 A CN 115842159A CN 202111117866 A CN202111117866 A CN 202111117866A CN 115842159 A CN115842159 A CN 115842159A
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Abstract
The invention discloses a polymer-based composite solid electrolyte and a preparation method and application thereof. Adding polyoxyethylene, polyvinylidene fluoride and lithium bistrifluoromethanesulfonylimide into acetonitrile, stirring, and adding MOF5-NH 2 And (3) obtaining mixed slurry, and volatilizing and drying to obtain the polymer-based composite solid electrolyte. The polymer-based composite solid electrolyte has higher ionic conductivity and wide electrochemical window, and can inhibit shuttle effect of polysulfide in a lithium-sulfur battery and improve the cycle stability of the battery.
Description
Technical Field
The invention belongs to the technical field of solid lithium batteries, and relates to a polymer-based composite solid electrolyte and a preparation method and application thereof.
Background
As an important support and auxiliary technology of new energy industries, electrochemical energy storage devices become a global research and development hotspot, and novel electrochemical energy storage devices are developing towards high specific energy, high safety, long cycle life and low cost. The lithium-sulfur battery has excellent theoretical specific capacity (1672 mAh/g), the theoretical specific energy density of the lithium-sulfur battery is as high as 2600Wh/kg, and the main active substance sulfur element has rich storage capacity, low price and easy preparation and acquisition, so the lithium-sulfur battery is considered to be a battery system with ideal application prospect.
Different from the lithium intercalation and deintercalation reaction of the traditional lithium ion battery, the lithium sulfur battery adopts sulfur or a sulfur-containing compound as a positive electrode, lithium as a negative electrode, and the electrolyte adopts a liquid organic compound, so that the mutual conversion of electric energy and chemical energy is realized through the fracture/generation of a sulfur-sulfur bond. During discharge, lithium ions are extracted from the negative electrode and migrate to the positive electrode, the sulfur-sulfur bond of the active material of the positive electrode is broken, and a plurality of lithium sulfide intermediate products, such as Li, are generated along with the oxidation-reduction process of a large number of intermediate products 2 S 8 、Li 2 S 6 、Li 2 S 4 Eventually form Li 2 S; on charging, li 2 And S is electrolyzed, and the released lithium ions return to the negative electrode again to be deposited as metal lithium or inserted into the negative electrode material.
The development of lithium-sulfur batteries still faces a plurality of challenges so far, and in a liquid electrolyte system, the utilization rate of active substances is low, the capacity attenuation is rapid, the cycle life is short, the self-discharge is rapid, the safety performance needs to be improved, and the further development and application of the lithium-sulfur batteries are limited. The reason is mainly because the elemental sulfur is used as the positive electrode, is an electron insulator, has low conductivity, and is combined with the final product Li 2 S 2 /Li 2 The density difference of S is large, obvious volume effect exists, the polysulfide intermediate product can be dissolved in liquid organic electrolyte, the polysulfide intermediate product can be transferred to a negative electrode in the charging process and reacts with unstable lithium metal surface through self-discharge, and a product returns to a positive electrode to be oxidized, so that the shuttle effect is formed repeatedly, the utilization rate of active substances is low, and the capacity loss and the cycle performance reduction of the battery are caused. In addition, the problems of interface instability and dendritic crystal always exist when the metal lithium is used as the negative electrode, the problems of thermal runaway, short circuit explosion and the like are easily caused, and the popularization and the application of the lithium-sulfur battery are also restricted. The currently reported inorganic solid electrolyte has high ionic conductivity, but has the problems of poor processability, difficult film formation, difficult ion transmission at a solid-solid interface between the electrolyte and an electrode and the like, and is not easy to be directly applied to a battery device. While organic polymer electrolytes are promising for use in battery devices, a single organic polymer solid electrolyte, such as polyethylene oxideAnd the like, the room-temperature ionic conductivity is low, and the shuttle effect and the lithium dendrite problem cannot be effectively inhibited. At present, one effective strategy for improving polymer electrolytes is to add fillers into the polymer electrolytes, so as to improve the ionic conductivity and mechanical properties of the polymer electrolytes. Yuan et al, by adding MOF5 material to polyethylene oxide (PEO), improve the ionic conductivity of PEO-based polymer electrolyte, the principle is that the MOF material contains a large amount of Lewis acid sites, lewis acid can not only coordinate with oxygen atoms with lone pair electrons on ether groups of PEO chains, reduce the crystallinity of PEO, but also interact with anions in lithium salt, promote the decomposition of lithium salt, and improve the ionic conductivity of polymer electrolyte (Journal of Power Sources 240 (2013) 653-658), but the addition of simple MOF material can not significantly improve the ionic conductivity, and can not effectively solve the problems of low oxidation voltage, lithium dendrite and the like of polymer-based solid electrolyte.
Disclosure of Invention
The invention aims to provide a polymer-based composite solid electrolyte and a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the technical scheme that:
the preparation method of the polymer-based composite solid electrolyte comprises the following steps:
adding Polyoxyethylene (PEO), polyvinylidene fluoride (PVDF) and lithium bistrifluoromethanesulfonylimide (LiTFSI) into acetonitrile, performing ball milling treatment, and adding MOF5-NH 2 Uniformly dispersing materials to obtain mixed slurry, pouring the mixed slurry into a mould, and volatilizing and drying to obtain the polymer-based composite solid electrolyte; the mixed slurry comprises, by mass, 90 parts of polyethylene oxide, 10 parts of polyvinylidene fluoride, 32.62 parts of lithium bistrifluoromethanesulfonimide, 150 parts of acetonitrile and MOF5-NH 2 5 parts of materials.
Preferably, the polyethylene oxide has an average molecular weight of 1000000Da.
Preferably, the ball milling stirring speed is 300-400 rpm, and the ball milling time is 8-12 h.
Preferably, the volatilization drying process is: drying at 30 deg.C under normal pressure for 3 hr, and drying at 60 deg.C under vacuum for 24 hr.
The invention also provides the polymer-based composite solid electrolyte prepared by the preparation method.
Further, the invention provides an application of the polymer-based composite solid electrolyte in preparation of a solid lithium-sulfur battery.
Compared with the prior art, the invention has the following advantages:
(1) The invention forms a three-dimensional structure by compounding PEO and PVDF, and introduces MOF5-NH 2 The material has a large number of Lewis acid sites, lewis acid can not only coordinate with oxygen atoms with lone pair electrons on ether groups of a PEO chain to reduce the crystallinity of PEO, but also interact with anions in lithium salt to promote the decomposition of the lithium salt and improve the ionic conductivity of the polymer electrolyte;
(2) According to the invention, the added PVDF insoluble long-chain polysulfide and the amino group introduced into MOF5 are polar groups, so that the shuttle effect of polysulfide can be effectively inhibited, and the cycle stability of the lithium-sulfur battery is improved;
(3) MOF5-NH added in the invention 2 The material contains amino groups, and can form hydrogen bonds with ether oxygen bonds in a polymer chain, so that the oxidation voltage of the polymer electrolyte is improved.
Drawings
Fig. 1 is an XRD spectrum of the polymer-based solid electrolytes prepared in comparative examples 1, 2, 3, 5 and example 1;
fig. 2 is an SEM image of the polymer-based solid electrolyte prepared in example 1;
fig. 3 is a graph comparing ionic conductivities of the polymer-based solid electrolytes prepared in comparative example 1 and example 1;
FIG. 4 is a comparison of electrochemical stability windows for semi-symmetrical cells assembled with polymer-based solid-state electrolytes prepared in comparative examples 1 and 5 and example 1, respectively;
fig. 5 is a graph comparing cycle performance of solid-state lithium-sulfur batteries assembled with polymer solid electrolytes prepared in comparative example 1 and example 1, respectively.
Detailed Description
The present invention will be described in further detail with reference to the following examples and the accompanying drawings.
MOF5-NH 2 The preparation method of (Energy Storage Materials 18 (2019) 59-67) comprises the following specific steps: 1.666g ZnNO 3 .6H 2 O and 0.36g H 2 Respectively dissolving ATA in 30ml DMF, stirring to dissolve ATA, transferring to a reaction kettle, placing in an oven at 120 deg.C for reaction for 12h, closing the oven and keeping the reaction kettle naturally cooling to room temperature in the oven; filtering out a crystal sample obtained by the reaction, washing the crystal sample with DMF repeatedly, drying the collected sample at 120 ℃, and finally collecting the sample for sealing and storing for use.
Comparative example 1
1g of polyethylene oxide (PEO) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were weighed into a ball mill pot containing 15g of acetonitrile and ball milled at 30 ℃ for 12h at 400rpm to form a clear viscous liquid. And then injecting the obtained transparent viscous liquid into a mold, drying at 30 ℃ under normal pressure for 3h to volatilize most of the solvent, then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24h to obtain the polymer-based composite solid electrolyte, and cutting the polymer-based composite solid electrolyte into small 16mm round pieces for later use.
Under the argon protection environment in a glove box, a Ketjen black/sulfur composite material is used as a positive electrode, and a lithium sheet is used as a negative electrode. After the prepared polymer-based solid electrolyte, the sulfur-carbon composite positive electrode and the negative electrode sheet are assembled into a button cell in a glove box, a charge-discharge cycle test is carried out on a LAND cell test system, and the working voltage is 1.6-2.8V (vs + )。
Comparative example 2
0.9g of polyethylene oxide (PEO), 0.1g of polyvinylidene fluoride (PVDF) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were weighed out and added to a ball mill pot containing 15g of acetonitrile, and ball milled at 30 ℃ for 12 hours at 400rpm to form a transparent viscous liquid. And then injecting the obtained transparent viscous liquid into a mold, drying at 30 ℃ under normal pressure for 3h to volatilize most of the solvent, then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24h to obtain the polymer-based composite solid electrolyte, and cutting the polymer-based composite solid electrolyte into small 16mm round pieces for later use.
Under the argon protection environment in a glove box, a Ketjen black/sulfur composite material is used as a positive electrode, and a lithium sheet is used as a negative electrode. After the prepared polymer-based solid electrolyte, the sulfur-carbon composite positive electrode and the negative electrode piece are assembled into a button cell in a glove box, a charge-discharge cycle test is carried out on a LAND cell test system, and the working voltage is 1.6-2.8V (vs + )。
Comparative example 3
1g of polyethylene oxide (PEO) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were weighed out into a ball mill pot containing 15g of acetonitrile and ball milled at 30 ℃ for 12h at 400 rpm. After a clear viscous liquid had formed, 0.05g of MOF5-NH was added 2 The material was uniformly dispersed therein to give a tan slurry. And injecting the obtained brown mud into a mold, drying at 30 ℃ for 3h under normal pressure to volatilize most of the solvent, then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24h to obtain the polymer-based composite solid electrolyte, and cutting the solid electrolyte into small 16mm round pieces for later use.
Under the argon protection environment in a glove box, a Ketjen black/sulfur composite material is used as a positive electrode, and a lithium sheet is used as a negative electrode. After the prepared polymer-based solid electrolyte, the sulfur-carbon composite positive electrode and the negative electrode piece are assembled into a button cell in a glove box, a charge-discharge cycle test is carried out on a LAND cell test system, and the working voltage is 1.6-2.8V (vs + )。
Comparative example 4
0.5g of polyethylene oxide (PEO) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were weighed into a ball mill pot containing 15g of acetonitrile and ball milled at 30 ℃ for 12h at 400rpm to form a clear viscous liquid. And then injecting the obtained transparent viscous liquid into a mold, drying at 30 ℃ under normal pressure for 3h to volatilize most of the solvent, and then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24h, so that the membrane-shaped polymer-based composite solid electrolyte cannot be obtained.
Comparative example 5
0.9g of polyethylene oxide (PEO), 0.1g of polyvinylidene fluoride (PVDF) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were charged into a ball mill pot containing 15g of acetonitrile and ball milled at 30 ℃ for 12 hours at 400 rpm. After a clear viscous liquid had formed, 0.05g of MOF5 material was homogeneously dispersed therein to give a tan slurry. And injecting the obtained brown mud into a mold, drying at 30 ℃ for 3h under normal pressure to volatilize most of the solvent, then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24h to obtain the polymer-based composite solid electrolyte, and cutting the solid electrolyte into small 16mm round pieces for later use.
Under the argon protection environment in a glove box, a Ketjen black/sulfur composite material is used as a positive electrode, and a lithium sheet is used as a negative electrode. After the prepared polymer-based solid electrolyte, the sulfur-carbon composite positive electrode and the negative electrode sheet are assembled into a button cell in a glove box, a charge-discharge cycle test is carried out on a LAND cell test system, and the working voltage is 1.6-2.8V (vs + )。
Example 1
0.9g of polyethylene oxide (PEO), 0.1g of polyvinylidene fluoride (PVDF) and 0.3262g of lithium bistrifluoromethanesulfonimide (LiTFSI) were charged into a ball mill pot containing 15g of acetonitrile and ball milled at 30 ℃ for 12 hours at 400 rpm. After a clear viscous liquid had formed, 0.05g of MOF5-NH was added 2 The material was uniformly dispersed therein to give a tan slurry. And injecting the obtained brown slurry into a mold, drying at 30 ℃ under normal pressure for 3 hours to volatilize most of the solvent, then transferring into a vacuum drying oven at 60 ℃ for vacuum drying for 24 hours to obtain the polymer-based composite solid electrolyte, and cutting the polymer-based composite solid electrolyte into small 16mm round pieces for later use.
Under the argon protection environment in a glove box, a Ketjen black/sulfur composite material is used as a positive electrode, and a lithium sheet is used as a negative electrode. After the prepared polymer-based solid electrolyte, the sulfur-carbon composite positive electrode and the negative electrode sheet are assembled into a button cell in a glove box, a charge-discharge cycle test is carried out on a LAND cell test system, and the working voltage is 1.6-2.8V (vs + )。
Fig. 1 is a XRD comparison graph of the polymer-based solid electrolytes prepared in comparative example 1, comparative example 2, comparative example 3, comparative example 5 and example 3, and it can be seen that the crystallinity of the solid electrolyte is reduced by adding PVDF, and the crystallinity of the polymer-based solid electrolyte can be further reduced by further adding MOF material, thereby improving the ionic conductivity of the solid electrolyte.
Fig. 2 is an SEM image of the polymer-based solid electrolyte prepared in example 1, and it can be seen that the composite polymer electrolyte has a smooth surface and less agglomeration because the metal-organic framework material has an organic-inorganic hybrid property and a small difference in surface energy with PEO, and thus can be uniformly dispersed in the PEO-LiTFSI polymer electrolyte.
FIG. 3 is a graph comparing the ionic conductivities of symmetrical batteries (stainless steel/composite solid electrolyte/stainless steel) assembled by the polymer-based composite solid electrolytes prepared in comparative example 1 and example 1 at 30-80 ℃, and it can be seen that the addition of PVDF and PEO form a three-dimensional structure to increase the ionic conductivity of the polymer electrolyte, and further added MOF5-NH 2 The material reduces the crystallinity of the obtained polymer-based solid electrolyte, thereby improving the ionic conductivity of the solid electrolyte. Comparative example 1 had an ionic conductivity of 10 at 30 deg.C -5.75 S.cm -1 And the ionic conductivity of example 1 reached 10 -4.9 S.cm -1 。
FIG. 4 shows semi-symmetrical cells (stainless steel/composite solid electrolyte/Li) assembled from polymer-based composite solid electrolytes prepared in comparative example 1, comparative example 5 and example 1, respectively, and having a voltage range of 2.5-6V and a sweep rate of 10mV s -1 Comparing the electrochemical stability windows measured under the conditions, the oxidation voltages of comparative example 1, comparative example 5 and example 1 are 3.7V, 4.7V and 5.3V respectively, and MOF5-NH can be seen 2 The addition of the material can improve the electrochemical stability of the polymer-based solid electrolyte.
Fig. 5 is a graph of long-term cycling performance of the all-solid-state lithium-sulfur battery assembled by the polymer-based solid electrolytes prepared in comparative example 1 and example 1 at 1.6-2.8V, 60 ℃ and 0.1C, and it can be seen that the solid-state lithium-sulfur battery assembled by the polymer-based solid electrolyte prepared in comparative example 1 shows poor cycling stability, after 50 cycles, the specific capacity is reduced to 400mAh/g, while the solid-state lithium-sulfur battery assembled by the polymer-based solid electrolyte prepared in example 1 shows better cycling stability. After 50 cycles at a current density of 0.1C, the capacity of example 3 still has 800mAh/g, which is only attenuated by 20%.
Claims (6)
1. The preparation method of the polymer-based composite solid electrolyte is characterized by comprising the following steps of:
adding polyoxyethylene, polyvinylidene fluoride and lithium bistrifluoromethanesulfonylimide into acetonitrile, carrying out ball milling treatment, and then adding MOF5-NH 2 Uniformly dispersing materials to obtain mixed slurry, pouring the mixed slurry into a mould, and volatilizing and drying to obtain the polymer-based composite solid electrolyte; the mixed slurry comprises, by mass, 90 parts of polyethylene oxide, 10 parts of polyvinylidene fluoride, 32.62 parts of lithium bistrifluoromethanesulfonimide, 150 parts of acetonitrile and MOF5-NH 2 5 parts of materials.
2. The method according to claim 1, wherein the polyethylene oxide has an average molecular weight of 1000000Da.
3. The preparation method of claim 1, wherein the ball milling stirring speed is 300-400 rpm, and the ball milling time is 8-12 h.
4. The method according to claim 1, wherein the volatilizing and drying process is: drying at 30 deg.C under normal pressure for 3 hr, and drying at 60 deg.C under vacuum for 24 hr.
5. The polymer-based composite solid electrolyte produced by the production method according to any one of claims 1 to 4.
6. Use of the polymer-based composite solid electrolyte according to claim 5 for the preparation of a solid-state lithium-sulfur battery.
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