CN109728342B

CN109728342B - Self-repairing composite solid electrolyte, quasi-solid electrolyte and lithium battery

Info

Publication number: CN109728342B
Application number: CN201811564924.9A
Authority: CN
Inventors: 刘巍; 夏水鑫
Original assignee: ShanghaiTech University
Current assignee: ShanghaiTech University
Priority date: 2018-12-20
Filing date: 2018-12-20
Publication date: 2021-11-16
Anticipated expiration: 2038-12-20
Also published as: CN109728342A

Abstract

The invention relates to the field of batteries, in particular to a self-repairing composite solid electrolyte, a quasi-solid electrolyte and a lithium battery. The self-repairing composite solid electrolyte comprises a self-repairing polymer and an inorganic solid electrolyte, wherein the self-repairing polymer comprises a self-repairing group, and the self-repairing group is selected from carbamido. The self-repairing composite solid electrolyte provided by the invention is bendable in dry basis and flexible, can inhibit the growth of lithium dendrites, has a self-repairing function, can prolong the service life of the battery, can keep higher conductivity by adding a small amount of lithium salt-containing electrolyte into the self-repairing composite solid electrolyte, can reduce the content of the lithium salt-containing liquid electrolyte, and can improve the safety of the battery.

Description

Self-repairing composite solid electrolyte, quasi-solid electrolyte and lithium battery

Technical Field

The invention relates to the field of batteries, in particular to a self-repairing composite solid electrolyte, a quasi-solid electrolyte and a lithium battery.

Background

Lithium metal has a high specific capacity (3860mAh g)^-1) And the lowest electrochemical potential (-3.040V vs. standard hydrogen electrode), are ideal negative electrode materials for the preparation of lithium batteries. However, the development of lithium metal batteries is limited by the uncontrolled lithium electrodeposition behavior during repeated delithiation/intercalation cycles resulting in the growth of lithium dendrites causing cell shorting and energy loss. Also, the generation of a Solid Electrolyte Interface (SEI) causes a decrease in the coulombic efficiency of the battery and a deterioration in the cycle performance of the battery. In addition, the infinite volume expansion of the lithium metal negative electrode causes the continuous accumulation of interfacial stress to cause the collapse of an SEI layer and the continuous increase of the interfacial resistance of the battery.

At present, methods for improving the stability of lithium metal negative electrodes mainly include: an artificial SEI layer, an interface protective layer, an electrolyte additive, etc. are introduced and a 3D lithium metal pillared material is constructed, however, the battery can only be used at a low current density due to the low conductivity of the interface layer and poor mechanical stability, and the battery performance is continuously degraded due to the continuous consumption of the electrolyte additive, and the energy density of the battery as a whole is reduced due to the introduction of the additional pillared material.

Disclosure of Invention

The invention aims to provide a self-repairing composite solid electrolyte, a quasi-solid electrolyte and a lithium battery.

To achieve the above and other related objects, an aspect of the present invention provides a self-repairing composite solid electrolyte including a self-repairing polymer including a self-repairing group selected from urea groups, and an inorganic solid electrolyte.

In some embodiments of the invention, at least a portion of the terminal groups of the self-healing polymer comprise the self-healing groups.

In some embodiments of the invention, the self-repairing polymer is selected from one or a combination of two of the compounds shown in formula 1 and formula 2,

in some embodiments of the invention, the self-repairing polymer is selected from a combination of a compound shown in a formula 1 and a compound shown in a formula 2, wherein the molar ratio of the compound shown in the formula 1 to the compound selected from the formula 2 is 1: 1-6: 1.

In some embodiments of the invention, the self-healing composite solid state electrolyte further comprises any one or more of the following conditions:

A1) the self-repairing composite solid electrolyte is a layer body, and the thickness of the self-repairing composite solid electrolyte is 10-80 microns, preferably 10-50 microns;

A2) the inorganic solid electrolyte is selected from oxides of cubic garnet structure, preferably from Ga_xLi_7- _3xLa₃Zr₂O₁₂Wherein x is more than or equal to 0 and less than or equal to 0.5, and the particle size of the inorganic solid electrolyte is 200-1000 nm;

A3) the mass percentage of the inorganic solid electrolyte in the self-repairing composite solid electrolyte is 10-50%, and preferably 20-40%.

Another aspect of the present invention provides a method for preparing a self-healing composite solid electrolyte, comprising: preparing inorganic solid electrolyte, adding the inorganic solid electrolyte into a self-repairing polymer to obtain a dispersion system, coating and drying.

Another aspect of the present invention provides a composite electrolyte, which includes the self-repairing composite solid electrolyte according to the present invention and a liquid electrolyte, the liquid electrolyte is 10% to 60% by mass of the composite electrolyte, and preferably 20% to 50% by mass of the composite electrolyte, and the liquid electrolyte includes a lithium salt.

Another aspect of the present invention provides a method for preparing a composite electrolyte, comprising: the self-repairing composite solid electrolyte provided by the invention is added with a liquid electrolyte containing lithium salt.

Another aspect of the invention provides the use of the self-healing composite solid electrolyte and/or composite electrolyte of the invention in a battery.

Another aspect of the present invention provides a lithium battery comprising the self-healing composite solid electrolyte according to the present invention and/or the composite electrolyte according to the present invention.

Drawings

FIG. 1 is a diagram of the self-healing mechanism of the present invention.

Fig. 2 is a Scanning Electron Microscope (SEM) image of the self-healing composite solid electrolyte of example 1 of the present invention.

Fig. 3 is an optical spectrum of the self-healing composite solid electrolyte of example 1 of the present invention.

Fig. 4 is a self-repairing optical spectrum of the self-repairing composite solid electrolyte of example 1 of the present invention.

Fig. 5 is a self-repairing Scanning Electron Microscope (SEM) spectrum of the self-repairing composite solid electrolyte of example 1 of the present invention.

Fig. 6 is a graph comparing the performance of lithium symmetrical batteries respectively prepared in example 7 of the present invention and comparative example 1.

FIG. 7 is a 0.2C first charge-discharge voltage curve for LTO/Li half cells prepared in example 8 of the present invention and comparative example 2, respectively.

FIG. 8 is a first charge-discharge voltage curve of LTO/Li half-cell 1C prepared according to example 8 of the present invention and comparative example 2, respectively.

FIG. 9 is a graph showing a comparison of the performance of LTO/Li half-cells of example 8 of the present invention and comparative example 2 at different rates.

FIG. 10 is a graph showing the first charge-discharge voltage of 0.2C LTO/Li half cell prepared in comparative example 3 according to the present invention.

Detailed Description

The self-healing composite solid electrolyte, quasi-solid electrolyte and lithium battery according to the present invention are described in detail below.

The invention provides a self-repairing composite solid electrolyte, which comprises a self-repairing polymer and an inorganic solid electrolyte, wherein the self-repairing polymer comprises a self-repairing group, and the self-repairing group is selected from carbamido. The self-repairing group of the self-repairing polymer can realize the self-repairing function of the electrolyte under the action of a hydrogen bond. Taking carbamido as an example, as shown in fig. 1, the hydrogen bond self-repairing mechanism is that carbamido forms a cross-linking structure through hydrogen bond combination, the sections are contacted after the material is damaged, and the self-repairing of the material is realized by utilizing the interaction between hydrogen bonds.

In the self-repairing composite solid electrolyte provided by the invention, at least part of the end groups of the self-repairing polymer comprise the self-repairing groups.

In the self-repairing composite solid electrolyte provided by the invention, the self-repairing polymer is selected from one or the combination of two of the compounds shown in the

formulas

1 and 2,

in the self-repairing composite solid electrolyte provided by the invention, the self-repairing polymer is selected from a combination of a compound shown as a formula 1 and a compound shown as a formula 2, wherein the molar ratio of the compound shown as the formula 1 to the compound shown as the formula 2 is 1: 1-6: 1, 1: 1-4: 1 or 4: 1-6: 1, and is preferably 4: 1.

In the self-repairing composite solid electrolyte provided by the invention, the film thickness of the composite solid electrolyte is 10-80 μm, 10-50 μm, or 50-80 μm, preferably 10-50 μm.

In the self-repairing composite solid electrolyte provided by the invention, the inorganic solid electrolyte is selected from cubic garnet-structured oxides. More particularly, the inorganic solid electrolyte is selected from gallium-doped lithium lanthanum zirconium oxides of the general formula GaxLi_7-3xLa₃Zr₂O12, wherein x is more than or equal to 0 and less than or equal to 0.5.

In the self-repairing composite solid electrolyte provided by the invention, the particle size of the inorganic solid electrolyte is selected from 200-1000 nm, 200-300 nm, 300-600 nm or 600-1000 nm, and preferably 300-600 nm.

In the self-repairing composite solid electrolyte provided by the invention, the mass percentage of the inorganic solid electrolyte in the self-repairing composite solid electrolyte is 10-50%, 10-20%, 20-40% or 40-50%, and the mass percentage of the inorganic solid electrolyte in the self-repairing composite solid electrolyte is preferably 20-40%. Within the mass ratio range, the self-repairing composite solid electrolyte can simultaneously have better mechanical property and self-repairing capability.

The second aspect of the present invention provides a method for preparing a self-healing composite solid electrolyte, comprising: preparing inorganic solid electrolyte, adding the inorganic solid electrolyte into a self-repairing polymer to obtain a dispersion system, and performing coating and drying treatment to obtain the electrolyte.

In the preparation method of the self-repairing composite solid electrolyte, the preparation of the inorganic solid electrolyte comprises the steps of dissolving gallium nitrate, lithium nitrate, lanthanum nitrate and zirconium acetylacetonate in an ethanol-water mixed solvent, controlling the volume ratio of ethanol to water to be 2: 1-5: 1, and adding citric acid to fully complex metal ions in the solution to obtain uniform sol. And heating the obtained sol at 60-90 ℃ for 4 hours, then heating to 180-200 ℃ for further heating for 8-12 hours to obtain gel, and finally fully drying at 200-250 ℃ to obtain dry gel. And calcining the obtained dried gel in a muffle furnace at 700-1000 ℃ for 4-6 hours, and cooling to obtain the oxide inorganic solid electrolyte.

In the preparation method of the self-repairing composite solid electrolyte provided by the invention, the preparation of the self-repairing composite solid electrolyte comprises the steps of uniformly dispersing a self-repairing polymer in a non-aqueous dispersing agent, adding an inorganic oxide electrolyte, stirring for 8-12 hours, stirring and heating at 50-100 ℃ to concentrate slurry, controlling the mass concentration of the slurry to be 40-60%, and standing the obtained slurry for 0-1 hour for defoaming treatment. And coating the slurry on a substrate by adopting a flat plate coating device, placing the obtained composite solid electrolyte membrane on a heating plate, drying for 10-12 hours at the temperature of 60-80 ℃, and then transferring the composite solid electrolyte membrane into a glove box filled with argon gas, and continuously drying for 8-10 hours at the temperature of 60-80 ℃ to obtain the self-repairing composite solid electrolyte.

In the preparation method of the self-repairing composite solid electrolyte provided by the invention, the dispersing agent in the preparation of the composite solid electrolyte is selected from one or more of N, N-dimethylformamide, N-methylpyrrolidone, acetonitrile, ethanol, dimethyl sulfoxide and acetone. The substrate is selected from one or more of polytetrafluoroethylene, copper foil and aluminum foil.

The third aspect of the invention provides a composite electrolyte, which comprises the self-repairing composite solid electrolyte and a liquid electrolyte, wherein the mass ratio of the liquid electrolyte in the composite electrolyte is 10% -60%, preferably 20% -50%, and the liquid electrolyte comprises a lithium salt. The composite electrolyte is a quasi-solid electrolyte which is a solid-liquid mixed electrolyte between a liquid electrolyte and an all-solid state, and can maintain the high mobility of the liquid electrolyte to the maximum extent and simultaneously has the long-term stability of the solid electrolyte.

In the composite electrolyte provided by the invention, the mass percentage of the liquid electrolyte in the composite electrolyte is 10-60%, 10-20%, 20-50%, 50-60%, preferably 20-50%.

In the composite electrolyte provided by the invention, the liquid electrolyte comprises a lithium salt, the lithium salt is selected from one or more of lithium bis (trifluoromethyl) sulfonyl imide, lithium nitrate, lithium hexafluorophosphate and lithium perchlorate, and the molar concentration of the lithium salt is selected from 0.5-1.5 mol L^-1。

In the composite electrolyte provided by the invention, a solvent in the liquid electrolyte is selected from one or more of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, 1, 3-dioxolane, ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

The fourth aspect of the invention provides a preparation method of the composite electrolyte, which comprises the step of adding a liquid electrolyte containing lithium salt to a dry base of the self-repairing composite solid electrolyte in a glove box to obtain the composite electrolyte, namely the quasi-solid electrolyte.

In the preparation method of the composite electrolyte, the addition amount of the liquid electrolyte containing lithium salt is 20-40 mu L.

In the preparation method of the composite electrolyte, the environment of the glove box is the glove box filled with argon and the oxygen value of the glove box is less than 1 ppm.

A fifth aspect of the invention provides the use of the self-healing composite solid electrolyte and/or composite electrolyte of the invention in a battery.

The invention also provides a lithium battery, which comprises a positive electrode, a negative electrode, the self-repairing composite solid electrolyte and/or the composite electrolyte.

In the lithium battery provided by the invention, the material of the positive electrode is selected from one or more of lithium cobaltate, lithium iron phosphate, lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, the positive electrode also comprises a binder and a conductive agent, the mass fraction of the binder is 5-15%, and the mass fraction of the conductive agent is 5-15%.

In the lithium battery provided by the invention, the negative electrode is selected from one or more of natural graphite, artificial graphite, lithium titanate, metallic lithium and silicon.

The invention has the beneficial effects that:

the self-repairing composite solid electrolyte provided by the invention is bendable, flexible, self-repairing and capable of inhibiting the growth of lithium dendrites, and has a self-repairing function so as to prolong the service life of the battery.

The composite electrolyte (namely, the quasi-solid electrolyte) has a self-repairing function due to the addition of the self-repairing composite solid electrolyte, the quasi-solid electrolyte has good conductivity, can stabilize a lithium metal negative electrode, can effectively inhibit the growth of lithium dendrites, reduces the reaction between metal lithium and an electrolyte, can reduce the content of a liquid electrolyte containing lithium salt, and improves the safety of a battery.

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

In the following examples, reagents, materials and instruments used therefor are commercially available without specific reference

Preparation of self-repairing composite solid electrolyte

Example 1

(1)Ga_0.25Li_6.25La₃Zr₂O₁₂Preparation of inorganic solid electrolyte

According to Ga_0.25Li_6.25La₃Zr₂O₁₂The stoichiometric ratio of the components is respectively called that gallium nitrate, lithium nitrate, lanthanum nitrate and zirconium acetylacetonate are uniformly dissolved in an ethanol-water mixed solvent, wherein the content of lithium nitrate needs to be excessive by 10 percent to make up for the loss of a lithium source in the high-temperature roasting process. The volume ratio of ethanol to water is 4:1, then citric acid is added to fully complex with cations in the solution to obtain white sol, then the white sol is heated for 4 hours at the temperature of 60 ℃, then the temperature is raised to 180 ℃, the white sol is heated for 10 hours to obtain gel, and the gel is fully dried at the temperature of 250 ℃ to obtain dry gel. And calcining the obtained dried gel in a muffle furnace at 800 ℃ for 5 hours to obtain the oxide solid electrolyte.

(2) Preparation of self-repairing composite solid electrolyte

Taking 0.3g of the compound shown in the formula 1 and the compound shown in the formula 2 according to a molar ratio of 4:1 in 1.2g of ethanol, and then 0.128g of Ga with the particle size of 500nm is added_0.25Li_6.25La₃Zr₂O₂Solid electrolyte, magnetic stirring at room temperature for 12 hours. And then placing the slurry on a heating plate at 60 ℃, stirring and concentrating until the mass concentration of the slurry is 40-50%, and then standing the slurry for 1 hour for degassing treatment. The slurry was uniformly coated on a teflon substrate by a plate coating method, and the thickness of the doctor blade was set to 250 μm. The slurry was uniformly applied to a substrate, and the film was allowed to stand for 2 hours, then transferred to a hot plate and heated at 60 ℃ for 10 hours, and then transferred to an argon-filled glove box (H)₂O≤1ppm，O₂Less than or equal to 1ppm) at 60 ℃ for 12 hours to fully dry.

Fig. 2 is a Scanning Electron Microscope (SEM) image of the self-healing composite solid electrolyte of example 1 of the present invention. As can be seen from fig. 2, the inorganic solid electrolyte particles are uniformly dispersed in the base of the polymer and have an average particle diameter of 500 nm.

Fig. 3 is an optical spectrum of the self-healing composite solid electrolyte of example 1 of the present invention. As can be seen from fig. 3, the self-healing composite solid electrolyte has good flexibility with an average thickness of 25 microns.

Fig. 4 is a self-repairing optical spectrum of the self-repairing composite solid electrolyte of example 1 of the present invention. As can be seen from fig. 4, the cracks in the electrolyte healed significantly after half an hour at room temperature and almost completely after two hours, demonstrating the self-healing capability of the self-healing composite solid electrolyte.

Fig. 5 is a self-repairing Scanning Electron Microscope (SEM) spectrum of the self-repairing composite solid electrolyte of example 1 of the present invention. As can be seen from fig. 5, after one hour, the fracture healed significantly, which further microscopically demonstrates the self-healing function of the self-healing composite solid electrolyte.

Example 2

(1)Ga_0.5Li_5.5La₃Zr₂O₁₂Preparation of inorganic solid electrolyte

According to Ga_0.5Li_5.5La₃Zr₂O₁₂The stoichiometric ratio of the components is respectively called that gallium nitrate, lithium nitrate, lanthanum nitrate and zirconium acetylacetonate are uniformly dissolved in an ethanol-water mixed solvent, wherein the content of lithium nitrate needs to be excessive by 10 percent to make up for the loss of a lithium source in the high-temperature roasting process. The volume ratio of ethanol to water is 4:1, then citric acid is added to fully complex with cations in the solution to obtain white sol, then the white sol is heated for 4 hours at the temperature of 60 ℃, then the temperature is raised to 180 ℃, the white sol is heated for 10 hours to obtain gel, and the gel is fully dried at the temperature of 250 ℃ to obtain dry gel. Will be describedThe obtained dry gel is placed in a muffle furnace to be calcined for 5 hours at 800 ℃ to obtain the oxide solid electrolyte.

(2) Composite solid electrolyte

0.3g of self-repairing polymer shown as the formula 1 is uniformly dissolved in 1.2g of ethanol, and then 0.128g of Ga with the particle size of 500nm is added_0.25Li_6.25La₃Zr₂O₂Solid electrolyte, magnetic stirring at room temperature for 12 hours. And then placing the slurry on a heating plate at 60 ℃, stirring and concentrating until the mass concentration of the slurry is 40-50%, and then standing the slurry for 1 hour for degassing treatment. The slurry was uniformly coated on a teflon substrate by a plate coating method, and the thickness of the doctor blade was set to 250 μm. The slurry was uniformly applied to a substrate, and the film was allowed to stand for 2 hours, then transferred to a hot plate and heated at 60 ℃ for 10 hours, and then transferred to an argon-filled glove box (H)₂O≤1ppm，O₂Less than or equal to 1ppm) at 60 ℃ for 12 hours to fully dry.

Example 3

(1)Ga_0.25Li_6.25La₃Zr₂O₁₂Preparation of inorganic solid electrolyte

According to Ga_0.25Li_6.25La₃Zr₂O₁₂The stoichiometric ratio of the raw materials is respectively called a certain amount of gallium oxide, lithium carbonate, lanthanum oxide and zirconium oxide, wherein the content of the lithium carbonate is excessive by 10 percent to make up for the loss of a lithium source in the high-temperature roasting process. The solid powder is firstly ball-milled for 15h and then roasted for 6h at 900 ℃, and then ball-milled for 15h to obtain electrolyte powder.

(2) Composite solid electrolyte

Dissolving 0.3g of self-repairing polymer compound shown as the formula 2 in 1.2g of ethanol, and then adding 0.3g of Ga_0.25Li_6.25La₃Zr₂O₂Solid electrolyte, magnetic stirring at room temperature for 12 hours. Then placing the slurry on a heating plate at 60 ℃, stirring and concentrating the slurry to the mass of the slurryThe concentration is 40-50%, and then the slurry is kept stand for 1 hour for degassing treatment. The slurry was uniformly coated on a teflon substrate by a plate coating method, and the thickness of the doctor blade was set to 250 μm. The slurry was uniformly applied to a substrate, and the film was allowed to stand for 2 hours, then transferred to a hot plate and heated at 60 ℃ for 10 hours, and then transferred to an argon-filled glove box (H)₂O≤1ppm，O₂Less than or equal to 1ppm) at 60 ℃ for 12 hours to fully dry.

Preparation of composite electrolyte (quasi-solid electrolyte)

Example 4

In a glove box filled with argon gas and having water and oxygen values less than 1ppm, 30 μ L of electrolyte containing lithium salt is added to the dry basis of the self-repairing composite solid electrolyte obtained in example 1, so as to obtain a quasi-solid electrolyte.

Example 5

In a glove box filled with argon gas and having water and oxygen values less than 1ppm, 30 μ L of electrolyte containing lithium salt is added to the dry basis of the self-repairing composite solid electrolyte obtained in example 2, so as to obtain a quasi-solid electrolyte.

Example 6

In a glove box filled with argon gas and having water and oxygen values less than 1ppm, 30 μ L of electrolyte containing lithium salt is added to the dry basis of the self-repairing composite solid electrolyte obtained in example 3, so as to obtain a quasi-solid electrolyte.

Preparation of three-lithium symmetrical battery and battery performance test

Example 7

In a glove box (H) filled with argon₂O≤1ppm，O₂Not more than 1ppm), assembling the lithium symmetrical battery in the order of the lithium sheet, the quasi-solid electrolyte of example 4 and the lithium sheet, standing the assembled battery for 0.5 hour, and then respectively keeping the room temperature at 3mA cm^-2-1mAh cm^-2，5mA cm^-2-1mAh cm^-2，10mA cm^-2-1mAh cm^-2，20mA cm^-2-1mAh cm^-2The charge and discharge performance of the battery was tested under the conditions of (1). The test results are shown in fig. 6.

Comparative example 1

In a glove box (H) filled with argon₂O≤1ppm，O₂Less than or equal to 1ppm), sequentially assembling the lithium symmetrical battery according to the sequence of a lithium sheet, a commercial Celgard 2325 diaphragm and the lithium sheet, standing the assembled battery for 0.5 hour, and respectively keeping the temperature at 1mA cm and cm at room temperature^-2-1mAh cm^-2，3mA cm^-2-1mAh cm^-2，5mA cm^-2-1mAh cm^-2，10mA cm^-2-1mAh cm^-2The charge and discharge performance of the battery was tested under the conditions of (1). The test results are shown in fig. 6.

Fig. 6 is a graph comparing the performance of lithium symmetrical batteries respectively prepared in example 7 of the present invention and comparative example 1. At 3mA cm^-2,1mAh cm^-2Under the conditions, no significant voltage fluctuation was observed in the first ten cycles of the lithium symmetric battery using the commercial Celgard 2325 separator, and the voltage fluctuation gradually increased after ten cycles. This indicates that the cell polarization is gradually larger with increasing cycle number. Especially at higher current densities (10mA cm)^-2，20mA cm^-2) Significant voltage fluctuations were observed, indicating that high current densities also increased the polarization of cells using commercial Celgard 2325 separator membranes. The lithium symmetrical battery adopting the quasi-solid electrolyte shows a stable charging and discharging platform in charging and discharging cycles, the voltage is still stable along with the increase of the cycle number, obvious voltage fluctuation is not observed, and the overpotential of the battery is far smaller than that of the lithium symmetrical battery adopting the commercial Celgard 2325 diaphragm. At 3mA cm^-2,1mAh cm^-2Under the conditions, the polarization of the lithium symmetrical cell using the quasi-solid electrolyte is only 36mV and can be stably cycled 1000 times. Especially at ultra high current densities (10mA cm)^-2，20mA cm^-2) Under the condition, the lithium battery adopting the quasi-solid electrolyte still shows lower overpotential, and a stable charging and discharging platform can be still observed, the overpotential of the lithium battery is obviously lower than that of a lithium symmetrical battery adopting a commercial Celgard 2325 diaphragm, wherein the overpotential is 10mA cm^-2-1mAh cm^-2The overpotential of the battery under the condition is 150mV and 20mA cm^-2-1mAh cm^-2The overpotential under the conditions was 240 mV. In particular at 20mA cm^-2-1mAh cm^-2The lithium battery adopting the mixed solid electrolyte can be stably circulated for 1500 times in an overlong way. Therefore, the lithium symmetric battery adopting the quasi-solid electrolyte shows better performance under the conditions of large multiplying power and long-time circulation. At the same time, the large capacity (10mA cm)^-2-10mAh cm^-2) Under the condition, the charge and discharge performance of the battery is improved, and the lithium symmetrical battery adopting the mixed solid electrolyte can stably circulate for 200 hours and shows smaller battery polarization. This indicates that lithium batteries employing quasi-solid electrolytes can provide ultra-high cell surface capacities in practical applications.

Preparation of LTO/Li half battery and battery performance test

Example 8

(1)Li₄Ti₅O₁₂Preparation method of electrode slice

Respectively weighing Li according to the mass ratio of 8:1:1₄Ti₅O₁₂Polyvinylidene fluoride (PVDF) and Super P, then adding an NMP solvent to prepare electrode slurry, placing the electrode slurry in a mixer, mixing for 30s at the rotating speed of 500rpm, then mixing for 10min at the rotating speed of 2000rpm, and degassing for 10min at the rotating speed of 2200rpm to obtain uniform electrode slurry.

And uniformly coating the slurry on a copper foil substrate by adopting a flat plate coating method, standing for 2 hours, and then transferring to a vacuum oven for drying at 60 ℃ for 12 hours. And (4) punching and cutting the dried electrode slice into a wafer with the diameter of 12mm after the electrode slice is rolled by a roll pair machine.

(2) Preparation of polyvinylidene fluoride film

Uniformly dissolving a certain amount of polyvinylidene fluoride in NMP solvent, and controlling the mass concentration of PVDF to be 0.05g ml^-1Then, it was uniformly coated on a glass substrate with a doctor blade thickness of 50 μm being controlled. The film was allowed to stand for 2 hours and then transferred to a vacuum oven for drying at 60 ℃ for 12 hours.

(3) Preparation of LTO/Li half-cell

In a glove box (H) filled with argon₂O≤1ppm，O₂Less than or equal to 1ppm), according to the lithium sheet and the composite electrolyte membrane (quasi-solid)Electrolyte in state), Li₄Ti₅O₁₂The lithium battery is assembled by the sequence of electrode plates. Among them, in a composite electrolyte membrane (quasi-solid electrolyte) and Li₄Ti₅O₁₂And adding a layer of PVDF film between the electrode plates, standing the assembled battery for 0.5 hour, and testing the electrochemical performance at room temperature under different multiplying powers, wherein the testing voltage is 1.1-2.4V.

Comparative example 2

In a glove box (H) filled with argon₂O≤1ppm，O₂Less than or equal to 1ppm), sequentially preparing a lithium sheet, a commercial Celgard 2325 diaphragm and Li₄Ti₅O₁₂The lithium battery is assembled by the sequence of electrode plates. And standing the assembled battery for 0.5 hour, and performing electrochemical performance tests at different multiplying powers at room temperature, wherein the test voltage is 1.1-2.4V.

Comparative example 3

In a glove box (H) filled with argon₂O≤1ppm，O₂Less than or equal to 1ppm), sequentially preparing a lithium sheet, a pure PVDF diaphragm and Li₄Ti₅O₁₂The lithium battery is assembled by the sequence of electrode plates. And standing the assembled battery for 0.5 hour, and performing electrochemical performance tests at different multiplying powers at room temperature, wherein the test voltage is 1.1-2.4V.

FIG. 7 is a 0.2C first charge-discharge voltage curve for LTO/Li half cells prepared in example 8 of the present invention and comparative example 2, respectively. As can be seen in fig. 7: the first discharge specific capacity of the LTO/Li half-battery adopting the commercial Celgard 2325 diaphragm under the condition of 0.2C is 149mAh g^-1In contrast, the first discharge specific capacity of the LTO/Li half-cell prepared using the quasi-solid electrolyte of example 8 based on example 4 was up to 157mAh g^-1The half cell based on a commercial Celgard 2325 separator exhibited a higher specific capacity at 0.2C than that exhibited with comparative example 2.

FIG. 8 is a first charge-discharge voltage curve under the condition of LTO/Li half-cell 1C prepared in example 8 of the present invention and comparative example 2, respectively. As can be seen from the figure: under the condition, the first discharge specific capacity of the half battery based on the commercial Celgard 2325 diaphragm is 129mAh g^-1And the first discharge ratio of the half-cell prepared using the quasi-solid electrolyte based on example 4The capacity can reach 143mAh g^-1And the specific discharge capacity of the half cell is obviously higher than that of the half cell adopting the commercial Celgard 2325 diaphragm.

FIG. 9 is a graph comparing the performance of LTO/Li half-cells prepared in example 8 of the present invention and comparative example 2 at different rates. As can be seen from the figure: the LTO/Li half-cells prepared with the quasi-solid electrolyte based on example 4 exhibited better rate performance than half-cells with Celgard separator.

FIG. 10 is a graph showing the first charge-discharge voltage of 0.2C LTO/Li half-cell of comparative example 3 according to the present invention. Comparative example 3 is the performance of an LTO/Li half cell using pure PVDF as the separator. As can be seen from fig. 10: LTO/Li half-battery adopting pure PVDF as diaphragm has first discharge specific capacity of only 128mAh g^-1The performance is lower than that of the LTO/Li half-cell prepared with a quasi-solid electrolyte based on example 4.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. Those skilled in the art can make various changes, modifications and equivalent arrangements, which are equivalent to the embodiments of the present invention, without departing from the spirit and scope of the present invention, and which may be made by utilizing the techniques disclosed above; meanwhile, any changes, modifications and variations of the above-described embodiments, which are equivalent to those of the technical spirit of the present invention, are within the scope of the technical solution of the present invention.

Claims

1. A lithium battery comprises a positive electrode, a negative electrode and a composite electrolyte, wherein a PVDF film is arranged between the composite electrolyte and the positive electrode; the composite electrolyte comprises a self-repairing composite solid electrolyte, the self-repairing composite solid electrolyte comprises a self-repairing polymer and an inorganic solid electrolyte, the self-repairing polymer comprises a self-repairing group, and the self-repairing group is selected from carbamido; the mass percentage of the inorganic solid electrolyte in the self-repairing composite solid electrolyte is 10-50%; the inorganic solid electrolyte is selected from oxides of cubic garnet structure;

the self-repairing polymer is selected from one or the combination of two of the compounds shown in the formulas 1 and 2,

2. the lithium battery of claim 1, wherein the self-healing polymer is selected from a combination of a compound represented by formula 1 and a compound represented by formula 2, and wherein the molar ratio of the compound represented by formula 1 to the compound represented by formula 2 is 1: 1-6: 1.

3. The lithium battery of claim 1, wherein the self-healing composite solid electrolyte is a layer, and wherein the thickness of the self-healing composite solid electrolyte is 10-80 μm.

4. The lithium battery as claimed in claim 3, wherein the self-healing composite solid electrolyte has a thickness of 10 to 50 μm.

5. Lithium battery according to claim 1, characterized in that the inorganic solid-state electrolyte is selected from Ga_xLi_7- _3xLa₃Zr₂O₁₂Wherein x is more than or equal to 0 and less than or equal to 0.5, and the particle size of the inorganic solid electrolyte is 200-1000 nm.

6. The lithium battery as claimed in claim 1, wherein the inorganic solid electrolyte accounts for 20-40% of the self-repairing composite solid electrolyte by mass.

7. The lithium battery as claimed in any one of claims 1 to 6, wherein the preparation method of the self-repairing composite solid electrolyte comprises the following steps: preparing inorganic solid electrolyte, adding the inorganic solid electrolyte into a self-repairing polymer to obtain a dispersion system, coating and drying.

8. The lithium battery as claimed in any one of claims 1 to 6, wherein the composite electrolyte further comprises a liquid electrolyte, the liquid electrolyte is 10 to 60% by mass of the composite electrolyte, and the liquid electrolyte comprises a lithium salt.

9. The lithium battery as claimed in claim 8, wherein the liquid electrolyte is 20 to 50% by mass of the composite electrolyte.

10. The lithium battery as claimed in claim 8, wherein the method of preparing the composite electrolyte comprises: and adding a liquid electrolyte containing lithium salt into the self-repairing composite solid electrolyte.