Polymer composite electrolyte membrane, method for preparing the same, and lithium metal battery

Abstract

The present application relates to the technical field of all-solid-state electrolyte, and particularly relates to a polymer composite electrolyte film, a preparation method thereof and a lithium metal battery. The polymer composite electrolyte film comprises a polymer, a lithium salt, an additive and a porous support body, wherein: the porous support body has high mechanical strength and electronic insulation, can enhance the mechanical properties of the polymer electrolyte, inhibit the formation of lithium dendrites and promote the uniform deposition of lithium, and the additive can generate an interface layer dominated by inorganic components in the battery cycle process, and inhibit the side reaction of the lithium negative electrode interface. The present application can solve the problem of the lack of preparation technology of high coulomb efficiency solid-state lithium battery, and under the joint action of the additive and the porous support body, the polymer composite electrolyte film has super-high lithium negative electrode stability and lithium metal negative electrode coulomb efficiency (98.64%), and significantly improves the cycle performance and safety of the lithium metal battery. The preparation process of the present application is simple and compatible with the existing process, and has great application prospect.

Description

Technical fields:

[0001] This invention relates to the field of all-solid-state electrolyte technology, specifically to a polymer composite electrolyte membrane, its preparation method, and a lithium metal battery. Background technology:

[0002] To develop high-energy-density and high-safety rechargeable battery systems, solid-state lithium metal batteries have become a frontier and hot topic in battery research. Solid electrolytes possess excellent thermal stability and are not prone to leakage, providing intrinsic safety for solid-state batteries. Meanwhile, lithium metal boasts a high theoretical specific capacity (3860 mAh g⁻¹). -1 With its low redox potential (-3.04V vs. standard hydrogen electrode), it is expected to increase battery energy density to over 300Wh / kg.

[0003] Solid electrolytes mainly include inorganic electrolytes and polymer electrolytes. Compared with inorganic electrolytes, polymer electrolytes have better chemical stability, processability, and better compatibility with lithium anodes, and therefore have received widespread attention. However, the practical application of polymer electrolytes in lithium metal batteries still faces two challenges: (1) The electrolyte undergoes chemical / electrochemical reactions with the highly reactive lithium metal anode, continuously generating a solid electrolyte interphase (SEI) layer, which consumes both lithium metal and electrolyte in the process. (2) Uneven lithium deposition leads to the formation of lithium dendrites, which are prone to detach from the current collector and break in the electrolyte, thus losing electrical contact and becoming "dead lithium," resulting in low coulombic efficiency and battery performance degradation. In addition, lithium dendrites may also penetrate the electrolyte, causing problems such as short circuits. The above challenges lead to irreversible loss of lithium metal anodes and low coulombic efficiency, making it impossible for polymer electrolytes to cycle stably in finite lithium full cells (N / P less than 10), hindering the practical application of high-energy-density solid lithium metal batteries. Therefore, optimizing the composition of polymer electrolytes to achieve uniform lithium deposition and high anode coulombic efficiency is of great significance.

[0004] In existing technologies, researchers have obtained stable SEIs rich in inorganic materials by introducing artificial interface layers or film-forming additives onto solid electrolytes [Adv. Energy Mater. 2023, 2203547.]. However, the aforementioned strategies for optimizing SEI composition still struggle to suppress lithium dendrite growth. To address this, researchers typically use inorganic fillers to improve the mechanical properties of polymer electrolytes. While this strategy can block lithium dendrite penetration to some extent, it cannot fundamentally solve the problem of uneven lithium deposition. Therefore, current work cannot effectively solve these problems and challenges, resulting in lithium anode coulombic efficiencies generally below 90%, making them unsuitable for batteries under limited lithium conditions. Summary of the Invention:

[0005] To address the lack of advanced technology for preparing high coulombic efficiency solid-state lithium batteries, this invention aims to provide a polymer composite electrolyte membrane, its preparation method, and a lithium metal battery. This electrolyte enables uniform lithium deposition, achieves ultra-high lithium anode coulombic efficiency (98.64%), and ultra-long lithium anode cycle time (3900 hours). Furthermore, when applied to low N / P (5.2) batteries, it can stably undergo 700 charge-discharge cycles.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a polymer composite electrolyte membrane, the method comprising the following steps:

[0008] (1) Dissolve the polymer, lithium salt and additives in a solvent in proportion, and stir until uniform to obtain a polymer electrolyte mixed solution;

[0009] (2) Coat the polymer electrolyte mixed solution obtained in step (1) onto the porous support, so that the polymer electrolyte solution permeates the porous support;

[0010] (3) After vacuum drying, the solvent is removed to obtain the polymer composite electrolyte membrane.

[0011] The polymer composite electrolyte membrane preparation method uses at least one of the following polymers: polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and propylene carbonate (PPC).

[0012] The method for preparing the polymer composite electrolyte membrane uses lithium salt selected from at least one of lithium bis(trifluoromethanesulfonate)imide (LiTFSI), lithium bis(fluorosulfonylimide) (LiFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), and lithium hexafluoroarsenate (LiAsF6).

[0013] The preparation method of the polymer composite electrolyte membrane uses at least one of lithium nitrate (LiNO3), silver nitrate (AgNO3), magnesium nitrate (Mg(NO3)2), copper nitrate (Cu(NO3)2), lithium bis(oxalate) difluorophosphate (LiDFBOP), fluoroethylene carbonate (FEC), and vinylene carbonate (VC).

[0014] The method for preparing the polymer composite electrolyte membrane uses at least one of acetonitrile, water, chloroform, acetone, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide as the solvent.

[0015] In the preparation method of the polymer composite electrolyte membrane, the weight of lithium salt is 10 wt.% to 50 wt.% of the total weight of polymer and lithium salt; the weight of additives is 1 wt.% to 40 wt.% of the total weight of polymer and lithium salt; and the weight of solvent is 5 to 100 times the weight of polymer.

[0016] Preferably, in step (1), the stirring time is 12 to 48 hours; in step (3), the drying temperature is 25 to 80°C and the drying time is 12 to 60 hours.

[0017] The method for preparing the polymer composite electrolyte membrane uses at least one of the following raw materials for the porous support: polyethylene, polypropylene, polyvinylidene fluoride-hexafluoropropylene, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyimide, glass fiber, alumina, and silicon dioxide.

[0018] The method for preparing the polymer composite electrolyte membrane describes a porous support having a connected pore network, with an average pore size of 10 nanometers to 10 micrometers and a porosity of 20% to 80%.

[0019] According to another aspect of the present invention, a polymer composite electrolytic membrane prepared by any of the methods described herein is provided.

[0020] According to another aspect of the present invention, the application of the polymer composite electrolyte membrane is provided in a lithium metal battery, which has a uniform and dense lithium deposition morphology, high lithium anode coulombic efficiency, and stable long-cycle performance.

[0021] According to another aspect of the present invention, a lithium metal battery is provided, comprising a positive electrode, a lithium negative electrode, and the polymer composite electrolyte membrane.

[0022] The design principle of this invention is as follows:

[0023] By utilizing additives in the polymer composite electrolyte membrane to participate in lithium-ion coordination and preferentially reduce lithium at the lithium anode side, a stable SEI rich in inorganic matter is formed, suppressing continuous side reactions between the lithium anode and the electrolyte. The porous support, with its high elastic modulus and nano-microscale continuous pores, promotes uniform lithium deposition at the anode and suppresses explosive dendrite growth. Furthermore, the porous support exhibits excellent electronic insulation, reducing the electronic conductivity of the composite electrolyte and mitigating lithium dendrite growth at the lithium anode interface and within the polymer electrolyte. Through the combined effect of the additives and the three-dimensional porous support, the coulombic efficiency and cycle life of the lithium metal battery are significantly improved. Therefore, this polymer composite electrolyte membrane ensures an efficient and stable lithium deposition / stripping process, resulting in high coulombic efficiency and long cycle life in solid-state lithium metal batteries using this polymer electrolyte.

[0024] The advantages and beneficial effects of this invention are as follows:

[0025] 1. This invention provides a polymer composite electrolyte membrane, which obtains a stable SEI layer rich in inorganic matter through additives, and promotes uniform deposition of lithium anode through a porous support with high elastic modulus and low electronic conductivity, thereby achieving an efficient and stable lithium deposition / stripping process.

[0026] 2. The polymer composite electrolyte membrane prepared by the method proposed in this invention can be used to assemble lithium-copper batteries with a coulombic efficiency of up to 98.64%, and the assembled lithium-lithium symmetric batteries can be stably cycled for more than 3900 hours.

[0027] 3. The all-solid-state coin cell lithium battery using this polymer composite electrolyte membrane can stably cycle 700 times under low N / P (5.2), and the all-solid-state soft-pack lithium battery can stably cycle 486 times under low N / P (7.6).

[0028] 4. The method for preparing polymer composite electrolyte membrane proposed in this invention has strong universality and low cost, is compatible with existing battery manufacturing processes, and is easy to scale up for mass production. Attached image description:

[0029] Figure 1 This is a photograph of the polymer composite electrolyte membrane prepared according to Example 1.

[0030] Figure 2 The cycle performance of the lithium-|| lithium symmetric batteries assembled according to Example 1, Comparative Example 1 and Comparative Example 2 is shown.

[0031] Figure 3 The coulombic efficiency of the lithium anode in the lithium-copper batteries assembled according to Example 1, Comparative Example 1, and Comparative Example 2 is given.

[0032] Figure 4 SEM image of the lithium deposition morphology on the copper foil surface after 5 charge-discharge cycles for the lithium||copper battery assembled according to Example 1.

[0033] Figure 5 The cycle performance of the solid-state coin cell assembled according to Example 5 at 60°C.

[0034] Figure 6 The charge-discharge curves of the solid-state pouch battery assembled according to Example 6 at 60°C with different charge-discharge cycles are shown. Detailed implementation method:

[0035] The following exemplarily illustrates the various steps involved in preparing the polymer composite electrolyte membrane and solid-state lithium metal battery of the present invention.

[0036] Example 1:

[0037] This embodiment describes the preparation of a polymer composite electrolyte membrane, and the process is as follows:

[0038] PEO, LiTFSI, and LiNO3, with a molecular weight of 6 million, were dissolved in acetonitrile and stirred for 24 hours to obtain a homogeneous polymer electrolyte mixture. PEO accounted for 7.9 wt.% of the polymer electrolyte mixture, LiTFSI accounted for 29 wt.% of the total mass of LiTFSI and PEO, and LiNO3 accounted for 5 wt.% of the total mass of LiTFSI and PEO. Subsequently, the polymer electrolyte mixture was coated onto a porous polyethylene support on a polytetrafluoroethylene sheet and dried at 60°C for 48 hours to obtain the polymer composite electrolyte membrane. The porous polyethylene support has an interconnected pore network with an average pore size of approximately 200 nm and a porosity of approximately 45%.

[0039] like Figure 1 The image shown is a physical picture of the polymer composite electrolyte membrane prepared by the present invention, which has a thickness of approximately 25 micrometers.

[0040] Comparative Example 1:

[0041] The difference between the comparative example and Example 1 is that the polymer electrolyte does not have a composite polyethylene porous support. Instead, an equivalent polymer electrolyte precursor liquid is directly coated onto a polytetrafluoroethylene sheet and then dried under the same conditions to obtain the polymer electrolyte of Comparative Example 1.

[0042] Comparative Example 2:

[0043] The difference between the comparative example and Example 1 is that the polymer electrolyte did not contain the additive LiNO3 and the polyethylene porous support. Instead, the polymer electrolyte precursor liquid was directly coated onto the polytetrafluoroethylene sheet and then dried under the same conditions to obtain the polymer electrolyte of Comparative Example 2.

[0044] Example 2:

[0045] This embodiment describes the preparation of a polymer electrolyte, and the process is as follows:

[0046] PEO (molecular weight 6 million), LiTFSI, and AgNO3 were dissolved in acetonitrile and stirred for 24 hours to obtain a homogeneous polymer electrolyte mixture. PEO accounted for 7.9 wt.% of the polymer electrolyte mixture, LiTFSI accounted for 40 wt.% of the total mass of LiTFSI and PEO, and AgNO3 accounted for 7 wt.% of the total mass of LiTFSI and PEO. Subsequently, the polymer electrolyte mixture was coated onto a porous polypropylene support on a polytetrafluoroethylene sheet and dried at 60°C for 48 hours to obtain a polymer composite electrolyte membrane with a thickness of approximately 25 micrometers. The porous polypropylene support has an interconnected pore network with an average pore size of approximately 100 nm and a porosity of approximately 55%.

[0047] Example 3:

[0048] This embodiment describes the preparation of a polymer electrolyte, and the process is as follows:

[0049] PVDF, LiTFSI, and FEC (with a molecular weight of 500,000) were dissolved in N-methylpyrrolidone solvent and stirred for 24 hours to obtain a homogeneous polymer electrolyte mixture. PVDF accounted for 7.9 wt.% of the polymer electrolyte mixture, LiTFSI accounted for 40 wt.% of the total mass of LiTFSI and PVDF, and FEC accounted for 10 wt.% of the total mass of LiTFSI and PVDF. Subsequently, the polymer electrolyte mixture was coated onto a three-dimensional porous polyethylene support on a polytetrafluoroethylene sheet. After drying at 60°C for 48 hours, the polymer composite electrolyte membrane with a thickness of 30 micrometers was obtained. The porous polyethylene support has an interconnected pore network with an average pore size of approximately 200 nm and a porosity of approximately 45%.

[0050] Example 4:

[0051] This embodiment describes the preparation of a lithium metal coin cell under limited lithium conditions. The process is as follows:

[0052] A positive electrode slurry was prepared by uniformly mixing lithium iron phosphate, polyvinylidene fluoride, conductive carbon black, and a polymer electrolyte mixture in N-methylpyrrolidone at a mass ratio of 7:1:1:1. This positive electrode slurry was then coated onto one side of a carbon-coated aluminum foil. The mixture was then vacuum-dried at 60°C to remove the N-methylpyrrolidone, yielding the positive electrode sheet. The polymer electrolyte mixture slurry refers to the mixed solution from Example 1.

[0053] The obtained composite positive electrode sheet was cut into electrodes with a diameter of 10 mm, and the active material mass was approximately 2.1 mg / cm³. 2 The negative electrode uses a pre-deposited 1.8mAh / cm 2Lithium-copper composite negative electrode. The polymer composite electrolyte membrane from Example 1 was sandwiched between the positive and negative electrode sheets and installed in a 2025 battery case to assemble a button cell for testing.

[0054] Example 5

[0055] This embodiment describes the preparation of a lithium metal pouch cell under limited lithium conditions. The process is as follows:

[0056] A positive electrode slurry was prepared by uniformly mixing lithium iron phosphate, polyvinylidene fluoride, conductive carbon black, and a polymer electrolyte slurry in N-methylpyrrolidone at a mass ratio of 7:1:1:1. This positive electrode slurry was then coated onto one side of a carbon-coated aluminum foil. The mixture was then vacuum-dried at 60°C to remove the N-methylpyrrolidone, yielding the positive electrode sheet. The polymer electrolyte slurry refers to the mixed solution from Example 1.

[0057] The obtained positive electrode was cut into positive electrode sheets (electrode sheet size 50mm × 64mm), with an active material mass of approximately 3.7 mg / cm³. 2 The negative electrode uses a 20-micron lithium-copper composite strip. The polymer composite electrolyte membrane from Example 1 is sandwiched between the positive and negative electrode sheets and encapsulated in aluminum-plastic composite to obtain a soft-pack battery for testing.

[0058] The following are the performance tests of the samples prepared in each embodiment:

[0059] 1. Lithium || Lithium Symmetric Battery Test:

[0060] The polymer composite electrolyte membrane prepared in Example 1 was used to form polymer composite electrolyte discs using a die-casting machine. The thickness of these discs was approximately 30 micrometers, and the disc diameter was 19 millimeters. A lithium-||lithium symmetric battery was assembled using the sample from Example 1, with 12-millimeter diameter lithium sheets added to both ends. Electrochemical performance was tested at 60°C. The samples in Comparative Examples 1 and 2 had a thickness of approximately 100 micrometers, with all other assembly conditions being the same. Figure 2 As shown, at a charging / discharging current density of 0.2 mA / cm² 2 Under test conditions with a charge-discharge time of 2 hours, the symmetrical batteries assembled in Comparative Examples 1 and 2 rapidly short-circuited due to uneven lithium deposition and uncontrolled dendrite growth. In contrast, the symmetrical battery assembled in Example 1 could cycle stably for 3900 hours. Thus, the polymer composite electrolyte membrane exhibits excellent lithium dendrite suppression capability.

[0061] 2. Lithium-copper battery testing:

[0062] The polymer electrolyte prepared in Example 1 was stamped using a stamping machine to obtain polymer electrolyte discs. The thickness of these discs was approximately 30 micrometers, and the disc diameter was 19 millimeters. A lithium-copper battery was assembled from the sample of Example 1, with a 12-millimeter diameter lithium sheet and a 16-millimeter diameter copper foil added to each end of the sample, respectively. The samples of Comparative Example 1 and Comparative Example 2 had a thickness of 100 micrometers, and all other assembly conditions were the same. Figure 3 As shown, at 60℃, the charge / discharge current density is 0.5 mA / cm². 2 Under test conditions of a 1-hour discharge time and a 1V charge cutoff voltage, the batteries assembled in Comparative Examples 1 and 2 exhibited low coulombic efficiency and poor cycle stability, while the battery assembled in Example 1 maintained stable cycling for 250 cycles with a high coulombic efficiency of 98.64%. The charge / discharge current density was 0.3 mA / cm² at 60°C. 2 Under the conditions of 1 hour discharge time and 1V charging cutoff voltage, 5 charge-discharge cycles were performed. In Example 1, the copper foil exhibited the characteristics of planar lithium growth and uniform deposition. Figure 4 This indicates that lithium dendrite growth was effectively suppressed. It is precisely due to the structural characteristics of the polymer composite electrolyte membrane involved in this invention that planar uniform lithium growth is promoted, dendritic growth is suppressed, and a more efficient lithium deposition / stripping process and stable cycling performance are achieved.

[0063] 3. Full battery cycle test:

[0064] The lithium metal battery prepared in Example 4 was tested at 60°C. The charging cutoff voltage was 4V, and the discharging cutoff voltage was 2.5V. The charge / discharge current was set to 0.5C (activation was performed 3 times at 0.2C). Figure 5 The figure shows the cycle performance of the full cell prepared according to Example 5 at an N / P ratio of 5.2. The coin cell containing this polymer composite electrolyte membrane maintained a discharge specific capacity of over 150 mAh / g and an average coulombic efficiency exceeding 99.94% after 700 charge-discharge cycles.

[0065] The lithium metal battery prepared in Example 5 was tested at 60°C. The charging cutoff voltage was 4V, and the discharging cutoff voltage was 2.5V. The charge / discharge current was set to 0.5C (activation was performed at 0.1C and 0.25C). Figure 6 As shown in the charge-discharge curves of the lithium metal battery prepared in Example 4 at different cycle numbers, the pouch battery containing this polymer composite electrolyte membrane still maintains a discharge specific capacity of over 118 mAh / g and an average coulombic efficiency of over 99.90% after 486 charge-discharge cycles. Therefore, this polymer composite electrolyte membrane has the potential to realize high-energy-density all-solid-state lithium batteries.

[0066] The results show that the porous support in the polymer composite electrolyte membrane provided by this invention possesses high mechanical strength and electronic insulation, which enhances the mechanical properties of the polymer electrolyte, inhibits the formation of lithium dendrites, and promotes uniform lithium deposition. The additives can generate an inorganic-dominated interface layer during battery cycling, suppressing side reactions at the lithium anode interface. This polymer composite electrolyte membrane exhibits ultra-high lithium anode stability and lithium metal anode coulombic efficiency (98.64%), significantly improving the cycle performance and safety of lithium metal batteries. The preparation process of this invention is simple and compatible with existing processes, showing great application potential.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that the above embodiments are exemplary and should not be construed as limiting the present invention. Several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polymer composite electrolyte membrane, characterized in that, The method includes the following steps: (1) Dissolve polyethylene oxide, lithium bis(trifluoromethanesulfonate)imide, and additives in a solvent in proportion, stir evenly to obtain a polymer electrolyte mixed solution, wherein the additives are at least one of lithium nitrate, silver nitrate, magnesium nitrate, and copper nitrate; the weight of lithium bis(trifluoromethanesulfonate)imide is 10 wt.% to 50 wt.% of the total weight of polyethylene oxide and lithium bis(trifluoromethanesulfonate)imide; the weight of the additives is 1 wt.% to 40 wt.% of the total weight of polyethylene oxide and lithium bis(trifluoromethanesulfonate)imide; and the weight of the solvent is 5 to 100 times the weight of polyethylene oxide. (2) The polymer electrolyte mixed solution obtained in step (1) is coated onto a porous support, allowing the polymer electrolyte mixed solution to permeate the porous support. The porous support has a network of interconnected pores, with an average pore size of 10 nanometers to 10 micrometers and a porosity of 20% to 80%. (3) After vacuum drying, the solvent is removed to obtain the polymer composite electrolyte membrane; By utilizing additives in polymer composite electrolyte membranes to participate in lithium ion coordination and preferentially reduce them on the lithium anode side, a stable solid electrolyte interface layer rich in inorganic matter is generated, which suppresses the continuous side reactions between the lithium anode and the electrolyte. Porous supports promote uniform lithium deposition at the anode, suppress explosive dendrite growth, reduce the electronic conductivity of the composite electrolyte, and alleviate lithium dendrite growth at the lithium anode interface and in the polymer electrolyte. With the combined effect of additives and three-dimensional porous supports, the coulombic efficiency and cycle life of lithium metal batteries are improved.

2. The method for preparing the polymer composite electrolyte membrane according to claim 1, characterized in that, The solvent is at least one of acetonitrile, water, chloroform, acetone, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide.

3. The method for preparing the polymer composite electrolyte membrane according to claim 1, characterized in that, The raw materials for preparing the porous support are at least one of polyethylene, polypropylene, polyvinylidene fluoride-hexafluoropropylene, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyimide, glass fiber, alumina, and silicon dioxide.

4. A polymer composite electrolyte membrane prepared by the method according to any one of claims 1 to 3.

5. A lithium metal battery, characterized in that, It includes the polymer composite electrolyte membrane as described in any one of claims 1 to 4.

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