WO2018233413A1

WO2018233413A1 - Method for protecting negative electrode of metal secondary battery by using polymer and application thereof

Info

Publication number: WO2018233413A1
Application number: PCT/CN2018/087100
Authority: WO
Inventors: 郭玉国; 王文鹏; 殷雅侠; 李林
Original assignee: 中国科学院化学研究所
Priority date: 2017-06-20
Filing date: 2018-05-16
Publication date: 2018-12-27
Also published as: CN109103517A; CN109103517B

Abstract

The present invention discloses a method for protecting a negative electrode of a metal secondary battery by using a polymer, allowing the protected negative electrode to be applied to a lithium metal secondary battery and a sodium metal secondary battery. The metal secondary battery protection method described in this patent is forming a polymer interface protective layer by ring-opening polymerization of a cyclic organic substance on the surface of a lithium metal or sodium metal negative electrode. The protection method has the advantage of being a simple technology and using easily available raw materials, and has high practical and commercialization potential. The application of the protected metal negative electrode to metal secondary batteries can significantly alleviate the common problem currently of dendritic crystallization in metal negative electrodes and can improve the cyclic performance and safety of batteries.

Description

Method for protecting polymer negative electrode of metal secondary battery and application thereof

Technical field

The invention belongs to the field of electrochemical power sources, relates to a method for protecting a negative electrode of a metal secondary battery, a novel polymer metal secondary battery using the method for protecting a negative electrode and an application thereof in an energy storage device.

Background technique

With the increase of population, the gradual increase of environmental climate problems and the depletion of resource reserves, the traditional energy structure based on coal, oil and natural gas has been severely challenged, and people are gradually turning to new types led by solar energy, wind energy and water energy. The energy system to get rid of dependence on traditional energy sources. However, such energy sources are intermittent in nature, and there is an urgent need to develop new energy storage devices to achieve large-scale real-time storage and release of energy to maintain an uninterrupted energy supply. As a typical representative of such energy storage devices, metal secondary batteries have made great progress in the past few decades, including lithium ion batteries, sodium ion batteries, lithium sulfur (selenium) batteries, sodium sulfur (selenium). A variety of systems including batteries, lithium air batteries, and sodium air batteries. At the same time, with the rapid rise of the electric vehicle field, the future society puts higher demands on the capacity and energy of the battery, which means that the metal secondary battery with high energy density is bound to stand out and occupy an important role in the future energy system. status. However, such batteries are inevitably dendritic, which greatly affects the safety and commercialization of metal secondary batteries.

In metal lithium and metal sodium secondary batteries, the uneven deposition of lithium ions and sodium ions leads to the formation of dendrites, which grow with the circulation and eventually pierce the separator and directly contact the positive electrode portion. A short circuit causes the battery to lose its performance, and more serious is a battery fire caused by a sudden release of heat at the moment of short circuit. In addition, the negative electrode that lacks protection will continuously react with the electrolyte to form a solid electrolyte interface (SEI) film. Due to the growth of dendrites, the interfacial reaction is repeated, so that the metal negative electrode is continuously involved in the reaction and is consumed, resulting in overall battery performance. The constant decay.

The current method for protecting the surface of the negative electrode includes covering the surface of the metal negative electrode with an inorganic interface layer, blocking direct contact between the negative electrode and the separator, and regulating uniform deposition of ions. Zhang's team (Adv.Mater.2016.28, 2888-2895) added a layer of glass fibers rich in polar functional groups between the lithium metal anode and the separator. The polar fibers can absorb lithium ions, thereby achieving lithium ion in the negative copper. A more even distribution of the foil surface prevents excessive local concentrations of lithium ions on the surface of the protrusion. However, this method requires the introduction of an additional layer of fiberglass, which is relatively complicated.

The invention creatively forms a polymer interface layer having a flat layer and a certain hardness and toughness on the surface of the metal secondary battery, and the force from the polymer layer can greatly inhibit the growth of dendrites, and at the same time, by means of the polymer and the metal anode The flat interface between the lithium ion and sodium ions can be more evenly distributed.

Summary of the invention

The present invention provides a method of protecting a negative electrode of a metal secondary battery using a polymer layer. The method for protecting the negative electrode of a metal secondary battery provided by the invention is as follows: a certain volume of the precursor solution is dropped on the surface of the metal negative electrode, and after a period of polymerization, the polymer protective layer is uniformly covered on the surface of the metal negative electrode. The polymer protective layer is prepared by: adding a precursor solution to the surface of the metal negative electrode under the protection of an inert gas, and after a period of polymerization, obtaining a metal negative electrode having a surface covering polymer protective layer, the precursor solution including at least Polymerization monomer, solvent, lithium salt three parts. The polymerizable monomer is one or more selected from the group consisting of cyclic ether organic compounds containing at least one oxygen atom. The volume fraction of the monomer is from 10% to 90%, preferably from 50% to 80%.

The polymer electrolyte includes at least a solvent, a monomer, and a lithium salt. The solvent is selected from the group consisting of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (ACN), dichloromethane (DCM), ethylene glycol dimethyl ether (DME), and triethylene glycol dimethyl ether. One or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate (PC). The volume fraction of the solvent is from 10% to 90%, preferably from 20% to 50%.

The cyclic ether organic material is selected from a C2-C20 cycloalkane containing at least one oxygen atom or a C3-C20 cyclic olefin having at least one oxygen atom. Preferably, the naphthenic ether organics are selected from (CH ₂ ) _n O _m monocycloalkane, C _n H _2n-2 O _m spiro or bridged cycloalkane having at least one oxygen atom, wherein 2≤n ≤20,1≤m≤6. Preferably, 2 ≤ n ≤ 12, 1 ≤ m ≤ 3. The volume fraction of the monomer is from 10% to 90%, preferably from 50% to 80%.

Preferably, the (CH ₂ ) _n O _m monocycloalkane organic substance having 1 oxygen atom is

The (CH ₂ ) _n O _m monocycloalkane organic substance having 2 oxygen atoms is

The (CH ₂ ) _n O _m monocycloalkane organic substance having 3 oxygen atoms is

Preferably, the C _n H _2n-2 O _m bridged cycloalkane ether organic material is selected from the group consisting of one oxygen atom.

Containing 2 oxygen atoms

Containing 3 oxygen atoms

Preferably, the C _n H _2n-2 O _m spirocycloalkane ether organic material is selected from the group consisting of one oxygen atom.

Containing 2 oxygen atoms

Containing 3 oxygen atoms

Preferably, at least one H on at least one carbon atom on the cycloalkane or cycloalkene ring may be substituted with an R group; the R group is selected from one of the following groups: an alkyl group, a cycloalkyl group , aryl, hydroxy, carboxy, amino, ester, halogen, acyl, aldehyde, decyl, alkoxy.

Preferably, the oxygen-containing cyclic ether organic material is selected from the group consisting of substituted ethylene oxide, substituted or unsubstituted oxetane, substituted or unsubstituted tetrahydrofuran, substituted or unsubstituted tetrahydropyran. The number of the substituents may be one or more; the substituent is the above R group.

The cyclic ether organic substance containing two oxygens is selected from a substituted or unsubstituted 1,3-dioxolane (DOL), a substituted or unsubstituted 1,4-dioxane ring; The number may be one or more; the substituent is the above R group.

The cyclic ether organic substance containing three oxygens is selected from substituted or unsubstituted terpolymeraldehyde; the number of the substituents may be one or more; and the substituent is the above R group.

Preferably, the monomer is selected from the group consisting of at least a mixture of the above two cyclic ether organics, including a mixture of ethylene oxide and 1,3-dioxolane, ethylene oxide and 1,4-dioxane. a mixture of cyclohexanes, a mixture of tetrahydrofuran and 1,3-dioxolane, a mixture of tetrahydrofuran and 1,4-dioxane, a mixture of tetrahydrofuran and trioxane, 1,3-dioxolane and trimer a mixture of formaldehyde. More preferably, the monomer is selected from the group consisting of a mixture of tetrahydrofuran and 1,3-dioxolane, a mixture of ethylene oxide and 1,3-dioxolane, a mixture of tetrahydrofuran and trioxane, tetrahydrofuran and 1 a mixture of 4-dihexylcyclohexane, at least one of a mixture of ethylene oxide and 1,4-dioxane. Wherein the volume ratio of ethylene oxide or tetrahydrofuran to 1,3-dioxolane or 1,4-dioxane is from 1:9 to 9:1, preferably from 1:3 to 3:1.

The lithium salt is lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonate)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, sodium perchlorate, lithium chloride, lithium iodide, and three (five) One or more of lithium fluoroethyl)trifluorophosphate and lithium dioxalate borate. Preferably, the lithium salt is one or more selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium chloride, and the like. The molar concentration of the lithium salt is from 0.2 to 7 M, preferably from 1.0 to 3.0 M. Preferably, the lithium salt is selected from the mixture of at least two lithium salts described above, including a mixture of lithium trifluoromethanesulfonate and lithium hexafluorophosphate, a mixture of lithium bis(trifluoromethanesulfonate) and lithium hexafluorophosphate, trifluoromethyl a mixture of lithium sulfonate and lithium tetrafluoroborate, a mixture of lithium bis(trifluoromethanesulfonate)imide and lithium tetrafluoroborate, a mixture of lithium trifluoromethanesulfonate and lithium perchlorate, and a bis(trifluoromethyl group) At least one of a mixture of lithium sulfinate and lithium perchlorate. More preferably, the lithium salt may be selected from the group consisting of lithium trifluoromethanesulfonate and a mixture of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonate)imide and lithium hexafluorophosphate, lithium trifluoromethanesulfonate and lithium tetrafluoroborate. Mixture, lithium bis(trifluoromethanesulfonate)imide and lithium tetrafluoroborate mixture. The molar concentration of lithium trifluoromethanesulfonate and lithium bis(trifluoromethanesulfonate)imide is 0.5-2.0 M, and the molar concentration of lithium hexafluorophosphate and lithium tetrafluoroborate is 0-0.05 M.

The inert gas includes various gases that do not react with the metal negative electrode, including one or more of argon, nitrogen, and helium.

The thickness of the polymer protective layer is from 10 μm to 100 μm, and the controllable condition is preferably from 10 μm to 50 μm. The thickness of the negative electrode side polymer protective layer is from 10 μm to 40 μm, preferably from 30 to 40 μm, and the thickness of the positive electrode side polymer protective layer is from 10 μm to 40 μm, preferably from 30 to 40 μm. The positive electrode side conductivity range is 6. × 10 ^-4 or more, preferably 10 ^{- 2} or more. The polymerization time is 2-100 h, preferably 3-24 h.

The reaction temperature at the time of polymerization is 10 to 40 ° C, preferably 15 to 30 ° C.

The invention also provides a novel polymer metal secondary battery, which is used as a method for protecting a negative electrode of a metal secondary battery.

The invention also provides a polymer metal secondary battery, the negative electrode material is a negative electrode which is surface-protected by the method as described above, the negative electrode metal is a metal lithium and a metal sodium negative electrode, and the positive electrode side is also dropped with a polymer precursor solution, the precursor The body solution is a precursor solution for protecting the surface of the negative electrode, wherein the positive electrode material comprises an embedded compound positive electrode material (such as lithium iron phosphate, lithium cobaltate, lithium manganate, ternary material, lithium-rich material, sodium manganate, sodium cobaltate, Sodium ferric phosphate, Prussian blue), oxide cathode material (manganese oxide, vanadium oxide), sulfur positive electrode, selenium positive electrode, lithium air positive electrode, sodium air positive electrode, etc.; separator including PP film, PE film, PP/PE film, PP/ PE/PP film, etc.

Further, the physical and chemical properties such as the degree of polymerization and the electrical conductivity of the positive electrode side electrolyte polymer are different from those of the negative electrode side polymer protective layer.

In addition, the above-mentioned application of the polymer metal secondary battery provided by the present invention in the preparation of a high energy density type energy storage device is also within the scope of protection of the present invention.

The method for protecting the negative electrode of a metal secondary battery by using the polymer layer provided by the invention has the advantages that the lithium ion and the sodium ion are effectively realized in the metal lithium and the metal by polymerizing a surface of the metal negative electrode to obtain a uniform polymer protective layer. Uniform deposition of the sodium surface; the polymer protective layer can exert a certain pressure on the surface of the negative electrode to inhibit the free growth of dendrites; the physical and chemical properties of the polymeric protective layer such as polymerization degree can be controlled by adjusting the ratio of the monomer to the solvent and the reaction conditions. Conductivity; the invention has the following advantages over the prior art: (1) The advantage of the invention is that it is not limited by the ability of the polymer to form a film, compared to the prior art in which the negative electrode is covered with a polymer film. The physical and chemical properties of the polymer layer can be flexibly adjusted. For example, the degree of polymerization and conductivity of the polymer can be freely adjusted, and the protective layer has better protection ability for the negative electrode than other polymer films covered by the negative electrode. (2) Compared with directly using the polymer as a solid electrolyte, it is advantageous in that a polymer having a different degree of polymerization and conductivity can be formed in the positive and negative electrodes, and a polymer battery having a polymerization degree gradient from the positive electrode to the negative electrode can be constructed. The polymer protective layer with high side polymerization degree can effectively protect the negative electrode, and the polymer with low polymerization degree on the positive electrode side does not affect the conductivity of the positive electrode, so that the battery has better performance (3) and other in situ coating on the negative electrode surface. Compared with the technology of the protective layer, the method has the advantages that the method is simple, the condition is mild, and the utility model has more practical value. Therefore, covering the surface of the negative electrode of the metal secondary battery with the polymer protective layer can solve the dendrite problem of the negative electrode of the metal secondary battery, thereby greatly improving the cycle stability and safety of the battery. In addition, the polymer protective layer is simple in preparation method, easy to obtain raw materials, and has high scale and commercialization prospects.

DRAWINGS

Figure 1 shows the charge and discharge curves of the polymer battery obtained in Example 1.

Figure 2a SEM of the surface of the polymer-protected lithium metal anode obtained in Example 1

Figure 2b SEM of a polymer-protected lithium metal anode obtained in Example 1

Figure 3a SEM picture of the surface of the metal lithium negative electrode after the polymer battery obtained in Example 1 is recycled

Figure 3b SEM image of the cross section of the lithium metal negative electrode after the polymer battery obtained in Example 1 is recycled

4 is a charge and discharge curve of a polymer battery in Comparative Example 1.

Figure 5a SEM image of the surface of the lithium metal negative electrode after cycling of the polymer battery obtained in Comparative Example 1.

Figure 5b SEM image of the cross section of the lithium metal negative electrode after the polymer battery obtained in Comparative Example 1

Detailed ways

The invention will now be further described in conjunction with specific embodiments.

The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available.

Example 1

(1) Preparation of polymer-protected lithium metal anode and polymer lithium battery

Step 1) Preparation of polymer-protected lithium metal anode: 40 μL of a precursor solution was added dropwise to the surface of the lithium sheet under a high-purity argon atmosphere, wherein the polymerized monomer was tetrahydrofuran, and the volume fraction was 80% of the total volume of the solution. The solvent is a 20% by volume EC/DEC/DMC mixed solvent (volume ratio 1:1:1), the lithium salt is a lithium hexafluorophosphate having a concentration of ¹ mol·L ^-1 , the reaction temperature is 25 ° C, and the reaction is allowed to stand for 20 hours, and the present invention can be obtained. A lithium negative electrode protected by a polymer interface layer. The surface of the polymer was observed by SEM to have a cross-sectional thickness of about 15 μ. The electrical conductivity of the obtained polymer was measured, and the test results are shown in Table 1. 2a is a SEM picture of the surface of the obtained polymer-protected metal lithium negative electrode, and FIG. 2b is a cross-sectional SEM picture of the obtained polymer-protected metal lithium negative electrode.

Step 2) Preparation of polymer electrolyte precursor solution: a polymer electrolyte precursor solution is prepared under a high purity argon atmosphere, wherein the polymerized monomer is tetrahydrofuran, the volume is 50% of the total volume of the solution, and the solvent is 50% by volume. The EC/DEC/DMC mixed solvent (volume ratio: 1:1:1) and the lithium salt was ¹ mol·L ^-1 of lithium hexafluorophosphate.

Step 3) Assembling the polymer battery: under high purity argon, using lithium iron phosphate as the positive electrode, adding 40 μL of the polymer electrolyte precursor obtained in the step 2) on the positive electrode side, and then sequentially adding the Celgard 2325 separator, and The polymer-protected lithium negative electrode obtained in the step 1) is sequentially stacked in the battery case in this order.

Step 4) In-situ polymerization: The battery case is completely sealed, and after waiting for the in-situ polymerization to be completed, a polymer lithium battery can be obtained.

(II) Electrochemical performance test of polymer lithium battery

The electrochemical performance of the battery was tested in a battery test system with a test voltage range of 2.5-4V. The test temperature was 25 ° C, and the battery capacity and charge and discharge current were calculated based on the mass of lithium iron phosphate. 1 is a charge and discharge curve of a polymer battery of Example 1 at a rate of 0.1 C. The test results of the obtained battery are shown in Table 1.

(III) Characterization of the morphology of the lithium metal anode side after circulation

After the above polymer battery was cycled for 100 cycles, the battery was disassembled in an argon glove box, and the dendrite growth of the surface and cross section of the metal lithium negative electrode was observed by a cold field emission scanning electron microscope (SEM). 3a is an SEM picture of the surface of the metal lithium negative electrode after the battery is circulated, and FIG. 3b is an SEM picture of the cross section of the metal lithium negative electrode after the cycle. The SEM image shows that after the polymer battery is circulated, no significant dendritic formation occurs on the surface of the negative metal lithium. The time required for the battery short circuit was measured at a 5 C charge and discharge rate. The test statistics are listed in Table 1.

Example 2

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 1) was 75%, and the volume fraction of the solvent was 25%. All test results are listed in Table 1.

Example 3

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 1) was 60%, and the volume fraction of the solvent was 40%. All test results are listed in Table 1.

Example 4

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 1) was 50%, and the volume fraction of the solvent was 50%. All test results are listed in Table 1.

Example 5

The other conditions were the same as in Example 1, except that the amount of the precursor solution added in the step 1) was 60 μL. All test results are listed in Table 1.

Example 6

The other conditions were the same as in Example 1, except that the amount of the precursor solution added in the step 1) was 50 μL. All test results are listed in Table 1.

Example 7

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 2) was 60%, and the volume fraction of the solvent was 40%. All test results are listed in Table 1.

Example 8

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 2) was 70%, and the volume fraction of the solvent was 30%. All test results are listed in Table 1.

Example 9

The other conditions were the same as in Example 1, except that the volume fraction of the polymerized monomer in the step 2) was 80%, and the volume fraction of the solvent was 20%. All test results are listed in Table 1.

Example 10

Other conditions are the same as in the first embodiment, except that the monomer type added in the step 1) is trioxane, and the type of the polymerization monomer added in the step 2) is trioxane. All test results are listed in Table 1.

Example 11

Other conditions were the same as in Example 1, except that the monomer type added in the step 1) was propylene oxide; and the type of the polymerized monomer added in the step 2) was propylene oxide. All test results are listed in Table 1.

Example 12

Other conditions are the same as in the first embodiment, except that the monomer type added in the step 1) is 1,4-dioxane; the type of the polymerization monomer added in the step 2) is 1,4-dioxane. ring. All test results are listed in Table 1.

Example 13

Other conditions are the same as in the first embodiment, except that the monomer type added in the step 1) is 1,3-dioxolane; the polymerization monomer added in the step 2) is 1,3-dioxol. ring. All test results are listed in Table 1.

Example 14

Other conditions were the same as in Example 1, except that the lithium salt used in the steps 1) and 2) was lithium perchlorate having a concentration of ¹ mol·L ^-1 . The test results for the obtained battery are shown in Table 1.

Example 15

Other conditions were the same as in Example 1, except that the lithium salt used in the step 1) and the step 2) was lithium hexafluoroborate having a concentration of ¹ mol·L ^-1 . The test results for the obtained battery are shown in Table 1.

Example 16

Other conditions were the same as in Example 1, except that the lithium salt used in the steps 1) and 2) was lithium chloride having a concentration of ¹ mol·L ^-1 . The test results for the obtained battery are shown in Table 1.

Example 17

Other conditions are the same as in the first embodiment except that the lithium salt in the step 1) and the step 2) is lithium hexafluoroborate having a concentration of 0.05 mol·L ^-1 and lithium lafluorotrifluoromethane 1.0 mol·L ^-1 . . The test results for the obtained battery are shown in Table 1.

Example 18

The other conditions were the same as in Example 1, except that the lithium salt in the step 1) and the step 2) was lithium hexafluoroborate having a concentration of 0.05 mol·L ^-1 and lithium perchlorate of 1.0 mol·L ^-1 . The test results for the obtained battery are shown in Table 1.

Example 19

Other conditions were the same as in Example 1, except that the lithium salt in the step 1) and the step 2) was a mixture of lithium tetrafluoroborate having a concentration of 0.05 mol of lithium trifluoromethanesulfonate and 1.0 mol·L ^-1 . The test results for the obtained battery are shown in Table 1.

Example 20

Other conditions were the same as in Example 1, except that the lithium salt in the step 1) and the step 2) was used in a concentration of 0.05 mol of lithium bis(trifluoromethanesulfonate)imide and 1.0 mol·L ^-1 of tetrafluoroboric acid. Lithium mixture. The test results for the obtained battery are shown in Table 1.

Example 21

The other conditions were the same as in Example 17, except that the monomer in the step 1) and the step 2) was a mixture of tetrahydrofuran and 1,3-dioxolane in a volume ratio of 1:1. The test results for the obtained battery are shown in Table 1.

Example 22

Other conditions were the same as in Example 17, except that the monomer was a mixture of ethylene oxide and 1,3-dioxolane in a volume ratio of 1:1. The test results for the obtained battery are shown in Table 1.

Example 23

The other conditions were the same as in Example 17, except that the monomer was a mixture of tetrahydrofuran and trioxane in a volume ratio of 1:1. The test results for the obtained battery are shown in Table 1.

Example 24

Other conditions were the same as in Example 17, except that the monomer was a mixture of tetrahydrofuran and 1,4-dioxane in a volume ratio of 1:1. The test results for the obtained battery are shown in Table 1.

Example 25

The other conditions were the same as in Example 17, except that the monomer was a mixture of ethylene oxide and 1,4-dioxane in a volume ratio of 1:1. The test results for the obtained battery are shown in Table 1.

Comparative example 1

(1) Preparation of polymer battery with unprotected lithium sheet as negative electrode

Step 1) Preparation of polymer electrolyte precursor solution: a polymer electrolyte precursor solution is prepared under a high purity argon atmosphere, wherein the polymerized monomer is tetrahydrofuran, the volume is 50% of the total volume of the solution, and the solvent is 50% by volume. The EC/DEC/DMC mixed solvent (volume ratio: 1:1:1) and the lithium salt was ¹ mol·L ^-1 of lithium hexafluorophosphate.

Step 2) Preparation of the cell: under high purity argon, lithium iron phosphate is used as the positive electrode, unprotected ordinary metal lithium is used as the negative electrode, and Celgard 2325 is used as the separator, which is sequentially stacked in the battery case in order to be injected into the cell. .

Step 3) Injecting liquid and in-situ polymerization: the polymer electrolyte precursor solution obtained in the step 1) is infiltrated into the cell obtained in the step 2). After the cell is completely infiltrated, the battery case is completely sealed, waiting for the in-situ polymerization to be completed. , a polymer lithium battery can be obtained.

(II) Electrochemical performance test of polymer lithium battery

The electrochemical performance of the battery was tested in a battery test system with a test voltage range of 2.5-4V. The test temperature was 25 ° C, and the battery capacity and charge and discharge current were calculated based on the mass of lithium iron phosphate. 4 is a charge and discharge curve of the polymer battery of Comparative Example 1 at a rate of 0.1 C. The test results of the obtained battery are shown in Table 1.

After the above polymer battery was cycled for 100 cycles, the battery was disassembled in an argon glove box, and the dendrite growth of the surface and cross section of the metal lithium negative electrode was observed by a cold field emission scanning electron microscope (SEM). Fig. 5a is an SEM picture of the surface of the metal lithium negative electrode after the battery cycle, and Fig. 5b is an SEM picture of the cross section of the metal lithium negative electrode after the cycle. The SEM image shows that after the polymer battery is circulated, there is a large amount of obvious dendrite formation on the unprotected negative metal lithium surface. The time required for the battery short circuit was measured at a 5 C charge and discharge rate. The test statistics are listed in Table 1.

Comparative example 2

(A) Battery preparation of a prior art polymer as an electrolyte

Step 1) Formulating a polymer precursor solution: preparing a polymer precursor solution under high purity argon, wherein the polymerized monomer is propylene oxide, the initiator is sodium ethoxide having a mass fraction of 1%, and the lithium salt is at a concentration of 1 mol·L. ^-1 lithium hexafluorophosphate. After stirring and mixing uniformly, a polymer precursor solution was obtained.

Step 3) Injecting liquid and in-situ polymerization: the polymer electrolyte precursor solution obtained in the step 1) is infiltrated into the cell obtained in the step 2). After the cell is completely infiltrated, the battery case is completely sealed, waiting for the in-situ polymerization to be completed. , a polymer lithium battery can be obtained. The test results of the obtained batteries are listed in Table 1.

In the battery of the present invention, the degree of polymerization of the negative electrode side polymer is preferably more than 30,000, more preferably more than 40,000, and the degree of polymerization of the polymer on the positive electrode side is preferably more than 18,000, more preferably 25,000, and the short circuit time is not less than 600 h, more preferably not less than 800 h. Most preferably, there is no short circuit, that is to say no short circuit within 1000 hours of the test. It can be seen that the battery material of the present invention has excellent electrical properties and can be easily used in practical applications.

Table 1 was analyzed: (1) Examples 1, 2, 3, and 4 were compared to illustrate the lithiation properties of the final polymer protective layer: such as the degree of polymerization, and the monomer of the precursor added dropwise at the negative electrode / The solvent ratio is related. When the monomer to solvent ratio is in the range of 4:1 to 3:1, the battery performance is good. When the monomer:solvent ratio is 4:1, the protection effect of the protective layer is the best; (2) Comparative Example 1, 5, 6, the thickness of the polymer protective layer is related to the amount of the precursor to which the negative electrode is dropped, and the thickness of the protective layer is 15 to 17 μm, which all show a good protective effect. (3) In Comparative Examples 1, 7, 8, and 9, it can be seen that the physical and chemical properties of the polymer electrolyte formed on the positive electrode side, such as electrical conductivity, can significantly affect the performance of the battery. The higher the conductivity of the electrolyte, the more favorable the performance of the positive electrode active material and the better the battery performance. At the same time, the change of the properties of the electrolyte on the positive electrode side does not affect the protective effect on the negative electrode. Therefore, considering the performance of the battery and the protection of the negative electrode, the monomer is selected on the positive electrode side: the polymer electrolyte having a solvent ratio of 1:1, and the negative electrode Side Selective Monomer: When the polymer protective layer has a solvent ratio of 4:1, it can be assembled into a polymer battery with the best performance. (4) Comparative Examples 1, 17, 18, 19, and 20, it can be seen that the use of the mixed lithium salt system is more advantageous for the performance of the battery than the single lithium salt system; (5) Comparative Example 17, 21, 22, 23, 24, and 25, it can be seen that the battery performance and the protective effect of the negative electrode are more excellent when the precursor of the mixed monomer is used than the single polymerization monomer system. Among them, the assembled polymer battery has the best performance by using a mixture of tetrahydrofuran and 1,3-dioxolane. (6) Comparing all of the above examples with Comparative Example 1, it can be seen that the growth of dendrites is effectively suppressed after the polymer protective layer is formed in situ on the surface of the negative electrode of the present invention. (7) Comparing all the examples provided by the present invention with Comparative Example 2 obtained by the prior art, it can be seen that the present invention proposes to form a polymer protective layer in situ on the negative electrode side, and introduce different in the positive and negative electrodes. The battery obtained by the conductivity of the polymer not only has no effect on the performance of the battery, but also the anode is effectively protected.

In summary, the present invention utilizes a ring-opening polymerization reaction of a cyclic organic substance to form a polymer layer on the surface of the metal negative electrode to effectively protect the surface of the metal negative electrode. The formed polymer protective layer can effectively inhibit the growth of dendrites, thereby greatly improving the cycle stability and safety of the metal secondary battery. The method is simple in operation, easy to obtain raw materials, and has remarkable effects, and is suitable for commercialized and large-scale applications.

The above is only a preferred embodiment of the present invention, and is not intended to limit the embodiments of the present invention. Those skilled in the art can make various modifications and changes to the present invention. The scope of protection shall be subject to the scope of protection required by the claims.

Claims

A method for protecting a surface of a negative electrode of a metal secondary battery, wherein a polymer protective layer is formed on the surface of the negative electrode, and the method for preparing the polymer protective layer is: adding a precursor solution on the surface of the metal negative electrode under the protection of an inert gas, after a period of time After polymerization, a metal negative electrode having a surface covering polymer protective layer is obtained. The precursor solution includes at least a polymerized monomer, a solvent, and a lithium salt. The polymerization monomer is selected from cyclic ethers containing at least one oxygen atom. One or more of the organic substances, the monomer may occupy a volume fraction of 10% to 90%, preferably 50% to 80%.
The method for protecting a surface of a negative electrode of a metal secondary battery according to claim 1, wherein the cyclic ether organic substance is selected from a C2 to C20 cycloalkane having at least one oxygen atom or at least one oxygen atom. C3-C20 cyclic olefin;

Preferably, the naphthenic ether organics are selected from (CH 2 ) n O m monocycloalkane, C n H 2n-2 O m spiro or bridged cycloalkane having at least one oxygen atom, wherein 2≤n ≤ 20, 1 ≤ m ≤ 6; preferably, 2 ≤ n ≤ 6, 1 ≤ m ≤ 3;

Preferably, at least one H on at least one carbon atom on the cycloalkane or cycloalkene ring may be substituted with an R group; the R group is selected from one of the following groups: an alkyl group, a cycloalkyl group , aryl, hydroxy, carboxy, amino, ester, halogen, acyl, aldehyde, decyl, alkoxy;

Preferably, the oxygen-containing cyclic ether organic material is selected from the group consisting of substituted ethylene oxide, substituted or unsubstituted oxetane, substituted or unsubstituted tetrahydrofuran, substituted or unsubstituted tetrahydropyran. The number of the substituents may be one or more; the substituents are the above R groups;

The cyclic ether organic substance containing two oxygens is selected from a substituted or unsubstituted 1,3-dioxolane (DOL), a substituted or unsubstituted 1,4-dioxane ring; The number may be one or more; the substituent is the above R group;

The cyclic ether organic substance containing three oxygens is selected from substituted or unsubstituted terpolymeraldehyde; the number of the substituents may be one or more; the substituents are the above R1 groups;

Preferably, the monomer is selected from the group consisting of at least a mixture of the above two cyclic ether organics, including a mixture of ethylene oxide and 1,3-dioxolane, ethylene oxide and 1,4-dioxane. a mixture of cyclohexanes, a mixture of tetrahydrofuran and 1,3-dioxolane, a mixture of tetrahydrofuran and 1,4-dioxane, a mixture of tetrahydrofuran and trioxane, 1,3-dioxolane and trimer a mixture of formaldehyde; more preferably, the monomer is selected from the group consisting of a mixture of ethylene oxide and 1,3-dioxolane, a mixture of ethylene oxide and 1,4-dioxane, tetrahydrofuran and 1, a mixture of 3-dioxolane, at least one of a mixture of tetrahydrofuran and 1,4-dioxane; wherein, ethylene oxide or tetrahydrofuran with 1,3-dioxolane or 1,4-di The volume ratio of the oxygen ring is 1:9-9:1, preferably 1:3-3:1;

The lithium salt is lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonate)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium chloride, lithium iodide, and three (five) One or more of lithium fluoroethyl)trifluorophosphate and lithium dioxalate borate; preferably, the lithium salt is one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium chloride, and the like. Or a plurality; the molar concentration of the lithium salt is 0.2-7M, preferably 1.0-3.0M;

Preferably, the lithium salt is selected from the mixture of at least two lithium salts described above, including a mixture of lithium trifluoromethanesulfonate and lithium hexafluorophosphate, a mixture of lithium bis(trifluoromethanesulfonate) and lithium hexafluorophosphate, trifluoromethyl a mixture of lithium sulfonate and lithium tetrafluoroborate, a mixture of lithium bis(trifluoromethanesulfonate)imide and lithium tetrafluoroborate, a mixture of lithium trifluoromethanesulfonate and lithium perchlorate, and a bis(trifluoromethyl group) At least one of a mixture of lithium sulfinate and lithium perchlorate; more preferably, the lithium salt may be selected from a mixture of lithium trifluoromethanesulfonate and lithium hexafluorophosphate, bis(trifluoromethanesulfonate)imide. a mixture of lithium and lithium hexafluorophosphate, a mixture of lithium trifluoromethanesulfonate and lithium tetrafluoroborate, a mixture of lithium bis(trifluoromethanesulfonate)imide and lithium tetrafluoroborate; wherein lithium trifluoromethanesulfonate, double ( The molar concentration of lithium trifluoromethanesulfonic acid)imide is 0.5-2.0 M, and the molar concentration of lithium hexafluorophosphate and lithium tetrafluoroborate is 0-0.05 M; the solvent is an organic solvent selected from dimethylformamide ( DMF), dimethyl sulfoxide (DMSO), acetonitrile (ACN), dichloromethane (DCM), ethylene glycol dimethyl ether (DME), three One of glycol dimethyl ether (TEGDME), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) Or several; the volume fraction of the solvent is from 10% to 90%; preferably, from 20% to 50%.
The method according to claim 1, wherein the inert gas comprises various gases which do not react with the metal negative electrode, including one or more of argon, nitrogen, and helium.
The method according to claim 1, wherein the polymer protective layer has a thickness of from 10 μm to 100 μm, preferably from 20 μm to 50 μm.
The process according to claim 1 wherein the polymerization time is from 2 to 100 h, preferably from 3 to 24 h.
The process according to claim 1, wherein the reaction temperature during the polymerization is 10 to 40 ° C, preferably 15 to 30 ° C.
A polymer metal secondary battery, the negative electrode material is a negative electrode surface-protected according to the method of any one of claims 1 to 6, the negative electrode metal is a metal lithium and a metal sodium negative electrode, and the positive electrode side is also dropwise added with a polymer precursor solution. The precursor solution is a precursor solution for protecting the surface of the negative electrode, wherein the positive electrode material comprises an embedded compound positive electrode material (such as lithium iron phosphate, lithium cobaltate, lithium manganate, ternary material, lithium-rich material, sodium manganate, sodium cobaltate) , sodium iron phosphate, Prussian blue), oxide cathode material (manganese oxide, vanadium oxide), sulfur positive electrode, selenium positive electrode, lithium air positive electrode, sodium air positive electrode, etc.; separator including PP film, PE film, PP/PE film, PP /PE/PP film, etc.
An energy storage device characterized by comprising the polymer metal secondary battery of any one of claims 7-8.