Solid-state electrolyte, preparation method and lithium ion battery

Abstract

A solid electrolyte, its preparation method, and a lithium-ion battery are disclosed, belonging to the field of solid electrolyte technology. This invention overcomes the shortcomings of existing PEO-based solid polymer electrolytes, such as low ionic conductivity and poor mechanical properties. The solid electrolyte of this invention comprises a crosslinked product of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, polypropylene carbonate, and a lithium salt; the average molecular weight of polyethylene glycol methyl ether acrylate is 300–500; the average molecular weight of polyethylene glycol diacrylate is 500–800; and the average molecular weight of the crosslinked product is 3000–6000.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology, specifically relating to a solid electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium is an ideal charge carrier, and in lithium metal batteries, metallic lithium, used as the negative electrode, has a very high charging capacity. However, during the charging process of lithium metal batteries, lithium ions are difficult to uniformly cover the surface of the negative electrode, leading to the growth of lithium dendrites. These dendrites can puncture the separator, causing a short circuit, or even causing the battery to swell or explode. Furthermore, the presence of lithium metal and organic solvents can cause fires. For these reasons, lithium metal negative electrodes have been replaced by graphite negative electrodes. While graphite is safer, its lithium-ion capacity is only 1 / 10 that of lithium metal negative electrodes, meaning that the charging capacity of these graphite-based batteries is about 9 times lower than that of lithium metal batteries. Lithium-ion batteries typically consist of a graphite negative electrode, a lithium metal oxide positive electrode, and an electrolyte. The electrolyte is the transport medium for lithium ions during charging and discharging; therefore, it is a crucial factor determining the energy storage capacity, safety, and stability of lithium-ion batteries. Most lithium-ion battery electrolytes consist of organic solvents and lithium salts dissolved in the organic solvent (e.g., lithium hexafluorophosphate, LiPF6), making them flammable and posing a risk of leakage. In addition, because these electrolytes are prone to decomposition due to electrolysis under high pressure, the overall voltage of the battery cannot be too high after it is made into a battery. Therefore, the positive electrode material of the battery can only be a low-pressure positive electrode material.

[0003] An effective way to solve the above problems is to use solid-state electrolytes to construct all-solid-state batteries. Solid-state electrolytes do not contain flammable solvents, meaning that solid-state batteries will be safer and cheaper than similar batteries; they also have better electrochemical stability than liquid electrolytes, making the use of high-voltage electrodes possible.

[0004] Among solid electrolytes, solid polymer electrolytes (SPEs) exhibit flexibility, ease of fabrication, and better interfacial stability with electrodes. Lithium ions have excellent complexation capabilities with polyethylene oxide (PEO) molecular chains, making PEO the most studied solid polymer electrolyte material; however, its ionic conductivity is relatively low (10⁻⁶). -7 ~10 -8Ion transport in PEO-based solid polymer electrolytes (SPEs) is generally related to the segmental motion of polymer chains. Due to the tight coordination between lithium ions and ether oxygen functional groups, the slow segmental motion of polymer chains and the increase in glass transition temperature (Tg) lead to a decrease in the ionic conductivity of PEO-based SPEs with increasing lithium salt concentration. Therefore, it is impossible to improve the ionic conductivity of PEO-based solid polymer electrolytes by increasing the lithium salt concentration. In the prior art, to reduce the crystallinity of PEO to promote its segmental motion and improve the ionic conductivity of PEO-based solid polymer electrolytes, fillers such as plasticizers, nanoparticles, or ionic liquids are used. However, since fillers generally have poor compatibility with PEO and are prone to agglomeration, a large number of defects are generated in the PEO solid electrolyte, resulting in reduced mechanical properties. This makes it difficult to process PEO-based solid electrolytes and assemble them into batteries; even when assembled into batteries, their cycle stability is poor. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low ionic conductivity and poor mechanical properties of PEO-based solid polymer electrolytes in the prior art, thereby providing a solid electrolyte, a preparation method and a lithium-ion battery.

[0006] To this end, the present invention provides the following technical solution.

[0007] On one hand, the present invention provides a solid electrolyte comprising a crosslinked product of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, polypropylene carbonate and lithium salt;

[0008] The average molecular weight of polyethylene glycol methyl ether acrylate is 300–500;

[0009] The average molecular weight of polyethylene glycol diacrylate is 500–800;

[0010] The average molecular weight of the crosslinked product is 3000 to 6000.

[0011] Furthermore, the crosslinking product contains 65-90% of the solid electrolyte by mass.

[0012] The polypropylene carbonate content is 5-20% of the solid electrolyte.

[0013] The lithium salt content is 5-15% of the solid electrolyte.

[0014] Furthermore, the lithium salt is LiClO4, LiPF6, or LiBF4.

[0015] Furthermore, the molecular weight of the polypropylene carbonate is 30,000 to 60,000.

[0016] Secondly, the present invention provides a method for preparing a solid electrolyte, comprising: mixing polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, adding a photoinitiator, performing ultraviolet light crosslinking, then adding polypropylene carbonate and lithium salt, stirring evenly, and solidifying to form a solid electrolyte.

[0017] Furthermore, the mass ratio of polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate, polypropylene carbonate and lithium salt is (45-80):(10-20):(5-20):(5-15).

[0018] Furthermore, polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate are first dissolved in an organic solvent and mixed and crosslinked, and then polypropylene carbonate and lithium salt are added to the above mixture.

[0019] Preferably, the organic solvent includes at least one of acetonitrile, o-dichlorobenzene, or n-butanol;

[0020] Preferably, the ratio of the total mass of polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate, polypropylene carbonate and lithium salt to the organic solvent is (1-4) g: (30-100) ml.

[0021] Furthermore, the photoinitiator is 0.5 to 0.8 wt% of the total weight of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate;

[0022] The photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone.

[0023] Furthermore, the UV curing wavelength for the UV crosslinking is 200–400 nm, and the time is 5–20 min;

[0024] After adding polypropylene carbonate and lithium salt, stir for 12–48 hours;

[0025] After stirring, the process also includes film formation at 60–90°C and vacuum drying for 24–48 hours.

[0026] Thirdly, the present invention also provides a lithium-ion battery comprising the above-described solid electrolyte or a solid electrolyte prepared by the above-described solid electrolyte preparation method.

[0027] Polyethylene glycol methyl ether acrylate (PEGMEA) is shown in formula a), polyethylene glycol diacrylate (PEGDA) is shown in formula b), and polypropylene carbonate (PPC) is shown in formula c). The crosslinking product of PEGMEA and PEGDA is XLPEO.

[0028] a)

[0029]

[0030] b)

[0031] c)

[0032]

[0033] The technical solution of this invention has the following advantages:

[0034] 1. The solid electrolyte provided by the present invention comprises a crosslinking product of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, polypropylene carbonate and lithium salt; the molecular weight of polyethylene glycol methyl ether acrylate is 300-500; the molecular weight of polyethylene glycol diacrylate is 500-800; and the molecular weight of the crosslinking product is 3000-6000.

[0035] This invention uses polyethylene glycol methyl ether acrylate (PPC) and polyethylene glycol diacrylate (PEG) as precursors to prepare crosslinked products. Both PPC and PEG contain ethylene oxide units, ensuring the complexation effect between the crosslinked products and lithium ions. During crosslinking, PPC exists in the form of branches and end groups, resulting in a large number of short branches within the system. The resulting segments have a high ether-oxygen bond content, reaching up to 82%, which helps suppress crystallinity, lowers the glass transition temperature, and improves ionic conductivity. The addition of PPC improves the mechanical properties of the solid electrolyte, facilitates material processing, and improves cycle stability and extends the actual battery life after assembly.

[0036] 2. The solid electrolyte provided by the present invention, wherein the lithium salt is LiClO4, LiPF6, or LiBF4, preferably LiClO4. The Li in LiClO4... + There is a coordination interaction between ClO4 and the carbonyl oxygen in PPC, which can significantly improve the mechanical properties of the entire polymer, thereby enhancing the cycle stability of the battery. - The larger particle size can repel PPC and cross-linking products, preventing the polymer from being too compact and affecting chain segment movement.

[0037] 3. The method for preparing solid electrolyte provided by the present invention includes: mixing polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, adding a photoinitiator, performing ultraviolet light crosslinking, without further separation, directly adding polypropylene carbonate and lithium salt, stirring evenly, and then solidifying to form solid electrolyte. The process is simple and the reaction conditions are relatively mild. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 LiClO4, PPC 20 XLPEO 75 Li5, XLPEO 95 Li5, PPC 70 Li 30 Infrared spectra of PPC and XLPEO.

[0040] like Figure 1 As shown, XLPEO (crosslinked product) at 1095 cm⁻¹ -1 The peaks for ether bonds are shown at the xlepse O3. 95 In the spectrum of Li5 (i.e., a solid electrolyte with 5% lithium salt content and the remainder being XLPEO), the peak shifts slightly to the left after the addition of 5 wt% LiClO4, indicating the interaction between ether bonds and Li. + There is an interaction between them. PPC at 1740cm -1 There is a spike at the point, PPC 70 Li 30 In the spectrum, the carbonyl oxygen broadened and shifted to the left after the addition of 30 wt% LiClO4, indicating that Li + It can also interact with the carbonyl oxygen of PPC. The spectrum of LiClO4 is shown at 1626 cm⁻¹. -1 There is a peak nearby that is not present in SPEs containing LiClO4; instead, it appears at 621 cm⁻¹ on these SPEs. -1 The peak at that point represents free ClO4. - Ions, confirming that LiClO4 dissociates into Li + and ClO4 - ion. Figure 1 This indicates that PPC is used here. 20 XLPEO 75 SPEs represented by Li5 contain carbonyl oxygen and ether oxygen. Detailed Implementation

[0041] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0042] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0043] Polyethylene glycol methyl ether acrylate was purchased from Anhui Zesheng Technology Co., Ltd., model E0807460250 (average molecular weight 300); polyethylene glycol diacrylate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model P131592 (average molecular weight 600); polypropylene carbonate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model P303235 (average molecular weight 50000).

[0044] Example 1

[0045] This embodiment provides a method for preparing a solid electrolyte, which includes the following steps:

[0046] 0.75 g of polyethylene glycol methyl ether acrylate and 0.1 g of polyethylene glycol diacrylate were dissolved in 50 ml of acetonitrile. Then, 0.0043 g of 1-hydroxycyclohexylphenyl ketone was added, and the mixture was crosslinked at a wavelength of 400 nm for 5 min in a UV apparatus (CX-2000, Ultra-Violet Products Ltd, Upland, CA). Then, 0.1 g of polypropylene carbonate and 0.05 g of LiClO4 were added and stirred for 24 h. The solution was poured between two glass plates spaced 200 μm apart and heated at 60 °C for 12 h to form a preliminary film. The film was then peeled off from the glass plates, placed on aluminum foil (to prevent adhesion to the petri dish), and vacuum dried at 60 °C for 48 h to completely remove the acetonitrile.

[0047] Example 2

[0048] This embodiment provides a method for preparing a solid electrolyte, which includes the following steps:

[0049] 0.65 g of polyethylene glycol methyl ether acrylate and 0.1 g of polyethylene glycol diacrylate were dissolved in 50 ml of acetonitrile. Then, 0.0043 g of 1-hydroxycyclohexylphenyl ketone was added, and the mixture was crosslinked at a wavelength of 400 nm for 10 min in a UV apparatus (CX-2000, Ultra-Violet Products Ltd, Upland, CA). Then, 0.2 g of polypropylene carbonate and 0.05 g of LiClO4 were added, and the mixture was stirred for 48 h. The solution was poured between two glass plates spaced 200 μm apart and heated at 80 °C for 12 h to form a preliminary film. The film was then peeled off from the glass plates, placed on aluminum foil (to prevent adhesion to the petri dish), and vacuum dried at 80 °C for 24 h to completely remove the acetonitrile.

[0050] Example 3

[0051] This embodiment provides a method for preparing a solid electrolyte, which includes the following steps:

[0052] 0.6 g of polyethylene glycol methyl ether acrylate and 0.2 g of polyethylene glycol diacrylate were dissolved in 30 ml of acetonitrile. Then, 0.0043 g of 1-hydroxycyclohexylphenyl ketone was added, and the mixture was crosslinked at a wavelength of 400 nm for 5 min in a UV apparatus (CX-2000, Ultra-Violet Products Ltd, Upland, CA). Then, 0.15 g of polypropylene carbonate and 0.05 g of LiClO4 were added, and the mixture was stirred for 24 h. The solution was poured between two glass plates spaced 200 μm apart and heated at 60 °C for 12 h to form a preliminary film. The film was then peeled off from the glass plates, placed on aluminum foil (to prevent adhesion to the petri dish), and vacuum dried at 60 °C for 24 h to completely remove the acetonitrile.

[0053] Example 4

[0054] This embodiment provides a method for preparing a solid electrolyte, which includes the following steps:

[0055] 0.75 g of polyethylene glycol methyl ether acrylate and 0.1 g of polyethylene glycol diacrylate were dissolved in 50 ml of n-butanol. Then, 0.0043 g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide was added, and the mixture was crosslinked at a wavelength of 400 nm for 5 min in a UV apparatus (CX-2000, Ultra-Violet Products Ltd, Upland, CA). Then, 0.1 g of polypropylene carbonate and 0.05 g of LiPF6 were added and stirred for 24 h. The solution was poured between two glass plates spaced 200 μm apart and heated at 60 °C for 12 h to form a preliminary film. The film was then peeled off from the glass plates, placed on aluminum foil (to prevent adhesion to the petri dish), and vacuum dried at 60 °C for 36 h to completely remove the n-butanol.

[0056] Example 5

[0057] This embodiment provides a method for preparing a solid electrolyte, which includes the following steps:

[0058] 0.75 g of polyethylene glycol methyl ether acrylate and 0.1 g of polyethylene glycol diacrylate were dissolved in 50 ml of o-dichlorobenzene. Then, 0.0043 g of 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone was added. The mixture was crosslinked at a wavelength of 400 nm for 5 min in a UV apparatus (CX-2000, Ultra-Violet Products Ltd, Upland, CA). Then, 0.1 g of polypropylene carbonate and 0.05 g of LiBF4 were added and stirred for 24 h. The solution was poured between two glass plates spaced 200 μm apart and heated at 60 °C for 12 h to form a preliminary film. The film was then peeled off from the glass plates, placed on aluminum foil (to prevent adhesion to the petri dish), and vacuum dried at 90 °C for 36 h to completely remove the o-dichlorobenzene.

[0059] Comparative Example 1

[0060] The solid electrolyte provided in this comparative example uses commercially available PEO (manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.; model: P101341) and LiClO4 doping, wherein the mass content of PEO is 95% and the mass content of LiClO4 is 5%.

[0061] Comparative Example 2

[0062] The preparation method of the solid electrolyte provided in this comparative example is basically the same as that in Example 1, except that PPC is not added.

[0063] Test case

[0064] The mechanical strength and lithium-ion conductivity of Examples 1-5 and Comparative Examples 1-2 were tested.

[0065] Mechanical property testing method: Solid electrolytes were cut into strips 3 cm long, 0.5 cm wide, and 0.02 cm thick, and then stretched at a speed of 5 mm / min (using a dynamic thermomechanical analyzer (Netzsch DMA242E)) to obtain their stress-strain behavior and then calculate their mechanical strength.

[0066] Ion conductivity testing method: The ionic conductivity of the material was measured by AC impedance spectroscopy using a Shanghai Chenhua CHI760E electrochemical workstation. The prepared sample was placed between two platinum wire electrodes and connected to the electrochemical workstation with wires. It was then placed in an oven at 70℃, and the impedance of the material was measured using the AC Impedance method. The frequency range was controlled between 1-10 Hz. 6 The frequency is Hz, the AC potential is controlled at 100mV, and the amplitude is set to 0.1V. The ionic conductivity of the material is calculated using the following formula:

[0067] σ=L / RA

[0068] In the formula: σ is the ionic conductivity (S cm⁻¹) -1 L is the distance between the two platinum electrodes (cm), and A is the cross-sectional area of ​​the sample in contact with the electrodes (cm²). 2 R is the resistance value of the sample (Ω).

[0069] Table 1 Performance of Solid Electrolytes

[0070] Young's modulus Fracture strain toughness Tensile strength Ion conductivity Example 1 23Mpa 30％ <![CDATA[380kJ / m 3 ]]> 1280kPa <![CDATA[7.2×10 -5 S cm -1 ]]> Example 2 37Mpa 50％ <![CDATA[480kJ / m 3 ]]> 1880kPa <![CDATA[2.4×10 -5 S cm -1 ]]> Example 3 20Mpa 33％ <![CDATA[350kJ / m 3 ]]> 1220kPa <![CDATA[1.6×10 -5 S cm -1 ]]> Example 4 13Mpa 17％ <![CDATA[306kJ / m 3 ]]> 1070kPa <![CDATA[8.1×10 -6 S cm -1 ]]> Example 5 16Mpa 24％ <![CDATA[290kJ / m 3 ]]> 960kPa <![CDATA[5.6×10 -6 S cm -1 <!-- 5 -->]]> Comparative Example 1 3.7 MPa 3％ <![CDATA[80kJ / m 3 ]]> 220kPa <![CDATA[5.2×10 -7 S cm -1 ]]> Comparative Example 2 7.7 MPa 15％ <![CDATA[140kJ / m 3 ]]> 530kPa <![CDATA[3.7×10 -6 S cm -1 ]]>

[0071] As shown in Table 1, the mechanical strength and ionic conductivity of the present invention are significantly improved.

[0072] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A solid electrolyte, characterized in that, Including cross-linked products of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, polypropylene carbonate and lithium salt; The average molecular weight of polyethylene glycol methyl ether acrylate is 300-500; The average molecular weight of polyethylene glycol diacrylate is 500-800; The average molecular weight of the crosslinked product is 3000~6000; The mass content of the crosslinking product is 65-90% of the solid electrolyte; The polypropylene carbonate content is 5-20% of the solid electrolyte. The lithium salt content is 5-15% of the solid electrolyte; The lithium salt is LiClO4; The molecular weight of the polypropylene carbonate is 30,000 to 60,000. The method for preparing the solid electrolyte includes: mixing polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate, adding a photoinitiator, performing ultraviolet light crosslinking, then adding polypropylene carbonate and lithium salt, stirring evenly, and solidifying to form a solid electrolyte; The mass ratio of polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate, polypropylene carbonate and lithium salt is (45~80):(10~20):(5~20):(5~15).

2. The solid electrolyte according to claim 1, characterized in that, First, polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate are dissolved in an organic solvent and mixed and crosslinked. Then, polypropylene carbonate and lithium salt are added to the above mixture.

3. The solid electrolyte according to claim 2, characterized in that, The organic solvent includes at least one of acetonitrile, o-dichlorobenzene, or n-butanol.

4. The solid electrolyte according to claim 2, characterized in that, The ratio of the total mass of polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate, polypropylene carbonate and lithium salt to the organic solvent is (1~4) g : (30~100) ml.

5. The solid electrolyte according to any one of claims 1-4, characterized in that, The photoinitiator is 0.5~0.8 wt% of the total weight of polyethylene glycol methyl ether acrylate and polyethylene glycol diacrylate; The photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, or 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone.

6. The solid electrolyte according to any one of claims 1-4, characterized in that, The UV curing wavelength for the UV crosslinking is 200~400 nm, and the time is 5~20 min; After adding polypropylene carbonate and lithium salt, stir for 12-48 h; After stirring, the process also includes film formation at 60-90 °C and vacuum drying for 24-48 h.

7. A lithium-ion battery, characterized in that, Includes the solid electrolyte as described in any one of claims 1-6.

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