PEO-based solid-state electrolyte, preparation method thereof and solid-state battery

Abstract

In view of the low ionic conductivity of the solid-state electrolyte in the prior art, the application provides a PEO-based solid-state electrolyte, a preparation method thereof and a solid-state battery. The PEO-based solid-state electrolyte comprises the following components: a parts of PEO, b parts of a lithium salt, c parts of a crosslinking agent, and d parts of a plasticizer, wherein the a, b, c and d need to satisfy the following relationship: 50 <= a <= 100, 10 <= b <= 50, 0.5 <= c <= 3 and 0.5 <= d <= 5. The PEO-based solid-state electrolyte provided by the application has high conductivity, high mechanical strength, good flexibility and film-forming property, and is easy to process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a PEO-based solid electrolyte, a preparation method thereof, and a solid-state battery. BACKGROUND

[0002] Secondary batteries in the prior art are widely used in technical fields such as portable electronic devices, electric vehicles, energy storage devices in hospitals and the like as energy storage equipment. Traditional secondary batteries include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte for conducting ions but insulating electrons. The traditional electrolyte is mostly an organic liquid electrolyte, and the organic liquid electrolyte has safety hazards such as swelling and liquid leakage during use.

[0003] A full solid-state battery is a new type of battery, and all components in the battery are solid. The main difference from the traditional battery is that a full solid-state electrolyte is used to replace the traditional liquid electrolyte and separator, which fundamentally changes the properties of the electrolyte and can better avoid the above problems. Although the solid-state electrolyte greatly improves the safety performance of the battery, there is a big problem with the solid-state electrolyte, that is, the ionic conductivity of the solid-state electrolyte is low. Most solid-state electrolytes are solid oxide electrolytes, such as NASICON-type Li 1+x Al x Ti 2x (PO4)(3LATP) and Li 1+x Al x Ge 2x (PO4)(3LAGP), garnet-type Li7La3Zr2O 12 (LLZO) and perovskite-type Li 3x La (2 / 3)-x TiO3(LLTO) has an ionic conductivity of about 10 -5 ~ 10 -3 S cm -1 , and the ionic conductivity is still relatively low. The ionic conductivity is an important indicator for measuring the electrical performance of the battery, and reflects the migration rate of ions inside the battery, which has an important influence on the charge and discharge rate of the battery. The low ionic conductivity of the fixed electrolyte limits the development of the full solid-state battery. SUMMARY

[0004] In view of the low ionic conductivity of the above solid-state electrolyte, the application provides a PEO-based solid electrolyte, which comprises the following components: a parts of PEO, b parts of lithium salt, c parts of crosslinking agent, d parts of plasticizer, and the a, b, c and d need to satisfy the following relationship:

[0005]

[0006] wherein 50≤a≤100, 10≤b≤50, 0.5≤c≤3, 0.5≤d≤5.

[0007] Preferably, the PEO has a molecular weight of 0.5 million to 5 million.

[0008] Preferably, the lithium salt comprises one or more of LiTFSI, LiClO4, LiBF4, LiAsF6, and LiPF6.

[0009] Preferably, the cross-linking agent comprises one or more of divinyl benzene, diisocyanate, N,N-methylene bisacrylamide, hydroxyethyl acrylate, glycidyl methacrylate, mercaptoacetic acid, and mercaptopropionic acid.

[0010] Preferably, the plasticizer comprises one or more of dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, dioctyl phthalate, butyl benzyl phthalate, di(2-ethyl)hexyl phthalate, and diisononyl phthalate.

[0011] In another aspect, the present application provides a method for preparing a PEO-based solid-state electrolyte, comprising the following steps:

[0012] adding a solvent into a reactor, and adding a portion of PEO and a portion of lithium salt into the reactor while stirring, to obtain a first mixed solution;

[0013] adding a portion of cross-linking agent and a portion of plasticizer into the first mixed solution, and introducing a protective gas, and then performing a heating and stirring reaction, to obtain a second mixed solution;

[0014] preparing a film from the second mixed solution, to obtain the PEO-based solid-state electrolyte;

[0015] the portions of a, b, c, and d satisfy the following relationship:

[0016]

[0017] wherein 50≤a≤100, 10≤b≤50, 0.5≤c≤3, 0.5≤d≤5.

[0018] Preferably, after adding the portion of lithium salt, the stirring time is 8h-12h.

[0019] Preferably, after introducing the protective gas, the heating temperature is 60℃-80℃, and the stirring time is 8h-12h.

[0020] Preferably, the solvent has a portion of 100-200 portions; and the solvent comprises one or more of methanol, ethanol, toluene, tetrachloromethane, acetonitrile, and tetrahydrofuran.

[0021] In another aspect, the application provides a solid-state battery, comprising a positive electrode, a negative electrode, and a PEO-based solid-state electrolyte disposed between and in contact with the positive electrode and the negative electrode, wherein the PEO-based solid-state electrolyte is the PEO-based solid-state electrolyte or is prepared by the method for preparing the PEO-based solid-state electrolyte.

[0022] Advantages:

[0023] Compared with the prior art, the PEO-based solid-state electrolyte provided by the application comprises a portion of PEO, b portions of lithium salt, c portions of crosslinking agent, and d portions of plasticizer, and satisfies the relationship The PEO chain segment regularity can be reduced, the crystallization can be inhibited, the glass transition temperature can be reduced, the movement ability of the PEO molecule can be improved, so that the PEO-based solid-state electrolyte has high electrical conductivity, high mechanical strength, good flexibility and film-forming property, and is easy to process. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and advantages of the application clearer, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0025] In one aspect, the application provides a PEO-based solid-state electrolyte, comprising the following components: a portions of PEO, b portions of lithium salt, c portions of crosslinking agent, and d portions of plasticizer, wherein the a, b, c and d satisfy the following relationship:

[0026]

[0027] wherein 50≤a≤100, 10≤b≤50, 0.5≤c≤3, and 0.5≤d≤5.

[0028] PEO is polyethylene oxide, and PEO is a polymer with the strongest complexing ability and is the most widely used polymer electrolyte matrix. The flexible polyether segment of the PEO molecule can complex with alkali metal ions (Li + ) under the action of an electric field. With the thermal motion of the molecules, Li + continuously undergoes a “coordination-dissociation” process with ether oxygen atoms, and directional and rapid migration of Li + is achieved through local relaxation and PEO segment movement, thereby producing ion conduction.

[0029] The PEO-based solid electrolyte is a crystalline polymer, and the PEO is not conducive to ion migration. In order to improve the ion conductivity of the PEO-based solid electrolyte, the inventors find through a large number of studies that, in the preparation process of the PEO-based solid electrolyte, a parts of PEO, b parts of lithium salt, c parts of crosslinking agent, and d parts of plasticizer are added, and the following relationship is satisfied The prepared PEO-based solid electrolyte can reduce the regularity of PEO segments, inhibit crystallization, reduce the glass transition temperature, and improve the movement ability of polymer molecules, so that the PEO-based solid electrolyte has high conductivity, high mechanical strength, good flexibility and film-forming property, and is easy to process; and has the effect of improving the cycle performance of the solid-state battery. If the PEO-based solid electrolyte does not satisfy the relationship The prepared PEO-based solid electrolyte has reduced conductivity, reduced cycle performance of the solid-state battery, reduced mechanical strength of the solid electrolyte, reduced film-forming property, increased manufacturing cost, and increased difficulty of use of the solid electrolyte film.

[0030] In some embodiments, the lithium salt includes one or more of LiTFSI, LiClO4, LiBF4, LiAsF6, and LiPF6.

[0031] The structure and concentration of the lithium salt affect the conductivity of the solid electrolyte system. In view of the influence of the structure of the lithium salt on the conductivity of the solid electrolyte system, the application adds the above-mentioned types of lithium salt to provide more carriers. Increasing the concentration of the lithium salt can increase the number of lithium ion migrations, but as the concentration of the lithium salt increases, the side effect is that the glass transition temperature (Tg) of PEO may increase, and salt ion complexation is intensified, which is not conducive to the thermal motion of PEO molecular chains, ion migration, film-forming property, and mechanical property. Therefore, the lithium salt b parts provided by the application is 10-50 parts, and the relationship a, b, c, d must be satisfied PEO cooperates with the lithium salt to improve the ion migration rate, so that the PEO-based solid electrolyte has high conductivity, high mechanical strength, and film-forming property. For example, the lithium salt can be 10 parts, 12 parts, 16 parts, 20 parts, 25 parts, 28 parts, 31 parts, 35 parts, 38 parts, 40 parts, 43 parts, 46 parts, 50 parts, etc., as long as the amount of the lithium salt is between 10 and 50 parts. More preferably, the amount of the lithium salt is 25-40 parts.

[0032] In some embodiments, the plasticizer includes one or more of dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, dioctyl phthalate, butyl benzyl phthalate, di(2-ethyl)hexyl phthalate, and diisononyl phthalate.

[0033] Specifically, PEO is a crystalline polymer, and the setting state is not conducive to ion migration, and the ion conductivity is low; therefore, for solid polymer electrolyte, inhibiting crystallinity and generating stable amorphous phase is the best way to improve ion conductivity. The inventors have found through a large number of studies that, in the preparation process of the PEO-based solid-state electrolyte, the addition of the above-mentioned plasticizer has the effects of reducing the glass transition temperature of PEO in the PEO-based solid-state electrolyte, increasing the amorphous content, improving the ion migration rate, and at the same time improving the flexibility of the PEO-based solid-state electrolyte film. It should be noted that the amount d of the plasticizer is 0.5 parts to 5 parts, and the requirements of a, b, c, and d must satisfy the relationship PEO cooperates with the plasticizer to improve the ion migration rate, ensure that the PEO-based solid-state electrolyte has high conductivity and flexibility, and is easy to process. For example, the amount of the plasticizer can be 0.5 parts, 0.8 parts, 1.0 part, 1.2 parts, 1.5 parts, 1.8 parts, 2.2 parts, 2.8 parts, 3.1 parts, 3.6 parts, 3.9 parts, 4.0 parts, 4.5 parts, 4.8 parts, 5.0 parts, etc. More preferably, the amount of the plasticizer is 1 to 4 parts.

[0034] The PEO-based solid-state electrolyte provided by the present application has high conductivity, high mechanical strength, good flexibility, and film-forming property, and is easy to process.

[0035] In some embodiments, the crosslinking agent includes one or more of divinylbenzene, diisocyanate, N,N-methylenebisacrylamide, hydroxyethyl acrylate, glycidyl methacrylate, mercaptoacetic acid, and mercaptopropionic acid.

[0036] Specifically, the crosslinking agent plays a crosslinking role in the preparation process of the PEO-based solid-state electrolyte, has the effect of enhancing the mechanical strength of the PEO-based solid-state electrolyte, and prevents the PEO-based solid-state electrolyte film from being broken during the preparation of the solid-state battery. The amount of the crosslinking agent c is 0.5 to 3, such as 0.5, 0.8, 1.0, 1.3, 1.6, 1.9, 2.2, 2.5, 2.8, 3.0, etc. More preferably, the amount of the crosslinking agent is 1.0 to 3 parts.

[0037] In another aspect, the present application provides a preparation method of a PEO-based solid-state electrolyte, which includes the following steps:

[0038] In the reactor, a solvent is added, and a portion of PEO a and a portion of lithium salt b are added during stirring to obtain a first mixed solution;

[0039] In the first mixed solution, a portion of the crosslinking agent c and a portion of the plasticizer d are added, and a protective gas is introduced, followed by heating and stirring reaction to obtain a second mixed solution;

[0040] The second mixed solution is prepared into a film to obtain the PEO-based solid-state electrolyte;

[0041] The terms a, b, c, and d need to satisfy the following relationship:

[0042]

[0043] Wherein, 50≤a≤100, 10≤b≤50, 0.5≤c≤3, and 0.5≤d≤5.

[0044] Specifically, the main steps of the method for preparing the second mixed solution into a film are: casting the second mixed solution into a polytetrafluoroethylene mold, evaporating the solvent, and further vacuum drying the obtained sample at 80°C for 2 hours to remove residual solvent, thereby obtaining a PEO-based solid electrolyte.

[0045] The method for preparing PEO-based solid electrolytes provided in this application is simple, low-cost, and easy to mass-produce. The prepared PEO-based solid electrolytes have high conductivity, high mechanical strength, good flexibility and film-forming properties, and are easy to process.

[0046] In some embodiments, the molecular weight of the PEO is 500,000 to 5,000,000.

[0047] The molecular weight of PEO affects the conductivity of PEO-based solid electrolytes. In this application, the molecular weight of PEO is controlled between 500,000 and 5,000,000, resulting in PEO-based solid electrolytes with high conductivity. The molecular weight of PEO can be between 500,000 and 1,000,000, 800,000 and 2,000,000, 1,500,000 and 3,000,000, 2,000,000 and 4,000,000, or 3,000,000 and 5,000,000, etc., and different molecular weights of PEO can be selected according to actual needs, as long as the molecular weight of PEO is between 500,000 and 5,000,000.

[0048] In some embodiments, after adding part b of lithium salt, the stirring time is 8h to 12h.

[0049] The stirring time can be 8h, 8.5h, 9.0h, 9.5h, 10.0h, 10.5h, 11h, 12h, etc., depending on the state of the solution during the stirring process.

[0050] In some embodiments, after introducing a protective gas, the heating temperature is 60°C to 80°C, and the stirring time is 8h to 12h.

[0051] The heating temperature can be 60℃, 62℃, 65℃, 68℃, 70℃, 73℃, 75℃, 79℃, or 80℃, and the stirring time can be 8h, 8.5h, 9.0h, 9.5h, 10.0h, 10.5h, 11h, or 12h, etc. The appropriate heating temperature and stirring time should be selected according to the actual amount of each substance added and the state of the solution.

[0052] Specifically, the protective gas includes inert gas or nitrogen, etc.

[0053] In some embodiments, the amount of the solvent is 100-200 parts; the solvent includes one or more of methanol, ethanol, toluene, tetrachloromethane, acetonitrile, and tetrahydrofuran.

[0054] In another aspect, the application also provides a solid-state battery, which comprises a positive electrode, a negative electrode, and a PEO-based solid-state electrolyte arranged between and in contact with the positive electrode and the negative electrode, wherein the PEO-based solid-state electrolyte is prepared by the above-mentioned method.

[0055] The positive electrode comprises a positive electrode material, and the positive electrode material comprises at least one of nickel-cobalt-manganese ternary material, lithium nickel cobalt manganese aluminum oxide, lithium nickel cobalt manganese oxide, sulfur-containing material, sodium-containing material, lithium-rich manganese material, lithium iron phosphate, lithium manganate, lithium cobaltate, lithium cobalt phosphate, lithium manganese nickel oxide, LiTiS2, and LiNiO2.

[0056] The negative electrode comprises a negative electrode material, and the negative electrode material comprises at least one of hard carbon, artificial graphite, natural graphite, lithium metal, carbon nanotube, and carbon nanofiber.

[0057] The solid-state battery provided by the application comprises a PEO-based solid-state electrolyte with high conductivity, which can improve the ion migration rate, reduce the interface impedance between the positive electrode, the negative electrode, and the PEO-based solid-state electrolyte, and improve the electrical performance of the battery.

[0058] The specific embodiment modes of the application will be further explained and described through the following examples, but the protection scope of the application is not limited in the range described in the examples.

[0059] Example 1

[0060] Preparation method of the PEO-based solid-state electrolyte:

[0061] In a reaction container, 100 parts of ethanol were added, and under constant stirring, a parts of PEO were added, followed by b parts of lithium salt selected from LiTFSI, and stirred for 12 h to obtain a first mixed solution. The molecular weight of the PEO was 3 million; a was 50 parts, and b was 10 parts.

[0062] In the first mixed solution, c parts of a crosslinking agent selected from hydroxyethyl acrylate and d parts of a plasticizer selected from diethyl phthalate were added, and then helium was introduced, heated to 60℃, and stirred for 10 h to obtain a second mixed solution; wherein c was 1 part, and d was 1 part.

[0063] The second mixed solution was cast into a polytetrafluoroethylene mold, the solvent was volatilized, and the obtained sample was further vacuum dried at 80°C for 2h to remove residual solvent, thereby obtaining a PEO-based solid-state electrolyte.

[0064] Preparation of a solid-state battery:

[0065] The PEO-based solid-state electrolyte described above was assembled with a positive electrode and a negative electrode to make a solid-state battery, and the electrical performance thereof was tested. The positive electrode comprises a positive electrode material, and the positive electrode material is lithium nickel cobalt manganese oxide. The negative electrode comprises a negative electrode material, and the negative electrode material is graphite. The preparation method of the positive electrode and the negative electrode refers to the prior art, and will not be described here.

[0066] Examples 2-8 and Comparative Examples 1-9

[0067] Examples 2-8 and Comparative Examples 1-9, which are different from Example 1 in that a, b, c, d are different, the types of lithium salt, crosslinking agent, and plasticizer are different, as shown in Table 1.

[0068] Table 1: PEO-based solid-state electrolyte parameter table of Examples 2-8 and Comparative Examples 1-9

[0069]

[0070]

[0071] Performance test:

[0072] (1) Test the ionic conductivity of the PEO-based solid-state electrolyte

[0073] The electrochemical impedance spectra of the solid-state batteries prepared in Examples 2-8 and Comparative Examples 1-9 were obtained, and the ionic conductivity was obtained. The test results are shown in Table 1.

[0074] (2) Test the cycle performance

[0075] The solid-state batteries prepared in Examples 2-8 and Comparative Examples 1-9 were tested for 500 cycle capacity retention at 25°C under normal temperature at 1C / 1C. The test results are shown in Table 2.

[0076] Table 2: Performance test table of Examples 2-8 and Comparative Examples 1-9

[0077]

[0078]

[0079] From Tables 1 and 2, it can be seen that Examples 1-8 and Comparative Examples 1-9 are compared, a, b, c, and d are all within the scope of the present application, but do not satisfy the relationship The prepared PEO-based solid electrolyte has a conductivity much lower than that of Examples 1-8, and the prepared solid-state battery has a low cycle capacity retention rate; it is indicated that the relations of a, b, c and d are not satisfied during the preparation of the PEO-based solid electrolyte The relations of a, b, c and d affect the conductivity of the PEO-based solid electrolyte and reduce the cycle performance of the battery.

[0080] In Comparative Examples 2-3, the amount of a PEO added is not within the range of 50-100 parts, the conductivity of the PEO-based solid electrolyte changes greatly, and the cycle performance is less affected. In Comparative Examples 4-5, the amount of b lithium salt added is not within the range of 10-50 parts, the content of the lithium salt is too high, and it is indicated that the side effects are that the glass transition temperature (Tg) of PEO may increase, and the complexation of salt ions is intensified, which is not conducive to the thermal motion of PEO molecular chains, ion migration, film formation and mechanical properties. Not only the conductivity of the solid electrolyte is reduced, but also the cycle performance is greatly reduced. In Comparative Examples 6-7, the amount of c crosslinking agent added is not within the range of 0.5-3, which affects the formation of the PEO-based solid electrolyte and its conductivity. In Comparative Examples 8-9, the amount of d plasticizer added is not within the range of 0.5-5, which also affects the conductivity and cycle performance of the solid electrolyte. It is speculated that the plasticizer affects the glass transition temperature of PEO in the PEO-based solid electrolyte, reduces the ion migration rate, and thus reduces the conductivity of the solid electrolyte.

[0081] From the above Tables 1 and 2, it is indicated that during the preparation of the PEO-based solid electrolyte, a PEO, b lithium salt, c crosslinking agent and d plasticizer are added, wherein 50≤a≤100, 10≤b≤50, 0.5≤c≤3, 0.5≤d≤5, and the relations of a, b, c and d are satisfied The prepared PEO-based solid electrolyte can reduce the regularity of PEO chain segments, inhibit crystallization, reduce the glass transition temperature, improve the movement ability of polymer molecules, so that the PEO-based solid electrolyte has high conductivity, high mechanical strength, good flexibility and film formation, and is easy to process; and has the effect of improving the cycle capacity retention rate of the battery.

[0082] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A PEO-based solid electrolyte, characterized in that, The product comprises the following components: a parts PEO, b parts lithium salt, c parts crosslinking agent, and d parts plasticizer, wherein a, b, c, and d must satisfy the following relationship: Wherein, 50≤a≤100, 10≤b≤50, 0.5≤c≤3, and 0.5≤d≤5.

2. The PEO-based solid electrolyte according to claim 1, characterized in that, The molecular weight of the PEO is between 500,000 and 5,000,000.

3. The PEO-based solid electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of LiTFSI, LiClO4, LiBF4, LiAsF6, and LiPF6.

4. The PEO-based solid electrolyte according to claim 1, characterized in that, The crosslinking agent includes one or more of divinylbenzene, diisocyanate, N,N-methylenebisacrylamide, hydroxyethyl acrylate, glycidyl acrylate, mercaptoacetic acid, and mercaptopropionic acid.

5. The PEO-based solid electrolyte according to claim 1, characterized in that, The plasticizer includes one or more of dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, dioctyl phthalate, butyl benzyl phthalate, di(2-ethylhexyl) phthalate, and diisononyl phthalate.

6. A method for preparing a PEO-based solid electrolyte according to any one of claims 1-5, characterized in that, Includes the following steps: A solvent is added to the reactor, and while stirring, a parts of PEO and b parts of lithium salt are added and stirred until homogeneous to obtain the first mixed solution. Add c parts of crosslinking agent and d parts of plasticizer to the first mixed solution, introduce a protective gas, and then heat and stir the reaction to obtain the second mixed solution; The second mixed solution was used to prepare a film to obtain a PEO-based solid electrolyte. The terms a, b, c, and d need to satisfy the following relationship: Wherein, 50≤a≤100, 10≤b≤50, 0.5≤c≤3, and 0.5≤d≤5.

7. The method for preparing the PEO-based solid electrolyte according to claim 6, characterized in that, After adding part b of lithium salt, the stirring time is 8h to 12h.

8. The method for preparing the PEO-based solid electrolyte according to claim 6, characterized in that, After introducing protective gas, the heating temperature is 60℃~80℃, and the stirring time is 8h~12h.

9. The method for preparing the PEO-based solid electrolyte according to claim 6, characterized in that, The solvent is present in an amount of 100 to 200 parts; the solvent includes one or more of methanol, ethanol, toluene, tetrachloromethane, acetonitrile and tetrahydrofuran.

10. A solid-state battery, characterized in that, The invention includes a positive electrode, a negative electrode, and a PEO-based solid electrolyte disposed on and in contact with the positive and negative electrodes respectively. The PEO-based solid electrolyte is the PEO-based solid electrolyte according to any one of claims 1-5 or prepared by the PEO-based solid electrolyte preparation method according to any one of claims 6-9.

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